Chapter 7: KINETIC ENERGY AND WORK

 

1. Which of the following is NOT a correct unit for work?

A. erg

B. ft·lb

C. watt

D. newton·meter

E. joule

                                                                                                                                          ans: C

 

2. Which of the following groups does NOT contain a scalar quantity?

A. velocity, force, power

B. displacement, acceleration, force

C. acceleration, speed, work

D. energy, work, distance

E. pressure, weight, time

                                                                     ans: B

 

3. A boy holds a 40-N weight at arm’s length for 10 s. His arm is 1.5m above the ground. The work done by the force of the boy on the weight while he is holding it is:

A. 0

B. 6.1J

C. 40 J

D. 60 J

E. 90 J

                                                                     ans: A

 

5. An object moves in a circle at constant speed. The work done by the centripetal force is zero

because:

A. the displacement for each revolution is zero

B. the average force for each revolution is zero

C. there is no friction

D. the magnitude of the acceleration is zero

E. the centripetal force is perpendicular to the velocity

                                                                     ans: E

 

6. An object of mass 1 g is whirled in a horizontal circle of radius 0.5m at a constant speed of 2m/s. The work done on the object during one revolution is:

A. 0

B. 1 J

C. 2 J

D. 4 J

E. 16 J

                                                                     ans: A (why is this true? asks the professor)

 

7. The work done by gravity during the descent of a projectile:

A. is positive

B. is negative

C. is zero

D. depends for its sign on the direction of the y axis

E. depends for its sign on the direction of both the x and y axes

                                                                     ans: A

 

8. A baseball is hit high into the upper bleachers of left field. Over its entire flight the work done by gravity and the work done by air resistance, respectively, are:

A. positive; positive

B. positive; negative

C. negative; positive

D. negative; negative

E. unknown since vital information is lacking

                                                                     ans: D

 

9. A line drive to the shortstop is caught at the same height as it was originally hit. Over its entire flight the work done by gravity and the work done by air resistance, respectively, are:

A. zero; positive

B. zero; negative

C. positive; negative

D. negative; positive

E. negative; negative

                                                                     ans: B

 

10. A 2-kg object is moving at 3m/s. A 4-N force is applied in the direction of motion and then removed after the object has traveled an additional 5m. The work done by this force is:

A. 12 J

B. 15 J

C. 18 J

D. 20 J

E. 38 J

                                                                     ans: D

 

11. A sledge (including load) weighs 5000 N. It is pulled on level snow by a dog team exerting a horizontal force on it. The coefficient of kinetic friction between sledge and snow is 0.05. How much work is done by the dog team pulling the sledge 1000m at constant speed?

A. 2.5 × 104 J

B. 2.5 × 105 J

C. 5.0 × 105 J

D. 2.5 × 106 J

E. 5.0 × 106 J

                                                                     ans: B

 

12. Camping equipment weighing 6000N is pulled across a frozen lake by means of a horizontal rope. The coefficient of kinetic friction is 0.05. The work done by the campers in pulling the equipment 1000m at constant velocity is:

A. 3.1 × 104 J

B. 1.5 × 105 J

C. 3.0 × 105 J

D. 2.9 × 106 J

E. 6.0 × 106 J

                                                                     ans: C

 

13. Camping equipment weighing 6000N is pulled across a frozen lake by means of a horizontal rope. The coefficient of kinetic friction is 0.05. How much work is done by the campers in pulling the equipment 1000m if its speed is increasing at the constant rate of 0.20m/s2?

A. 1.2 × 106 J

B. 1.8 × 105 J

C. 3.0 × 105 J

D. 4.2 × 105 J

E. 1.2 × 106 J

                                                                     ans: D

 

14. A 1-kg block is lifted vertically 1m by a boy. The work done by the boy is about:

A. depends on the time taken

B. 1 J

C. 10 J

D. 0.1J

E. zero

                                                                     ans: C

 

15. A 0.50-kg object moves in a horizontal circular track with a radius of 2.5m. An external force of 3.0N, always tangent to the track, causes the object to speed up as it goes around. The work done by the external force as the mass makes one revolution is:

A. 24 J

B. 47 J

C. 59 J

D. 94 J

E. 120 J

                                                                     ans: B

 

17. A man pushes an 80-N crate a distance of 5.0m upward along a frictionless slope that makes an angle of 30with the horizontal. His force is parallel to the slope. If the speed of the crate decreases at a rate of 1.5m/s2, then the work done by the man is:

A. 200 J

B. 61 J

C. 140 J

D. 200 J

E. 260 J

                                                                     ans: C

 

18. A man pushes an 80-N crate a distance of 5.0m upward along a frictionless slope that makes an angle of 30with the horizontal. The force he exerts is parallel to the slope. If the speed of the crate is constant, then the work done by the man is:

A. 200 J

B. 61 J

C. 140 J

D. 200 J

E. 260 J

                                                                     ans: D

 

19. An 80-N crate slides with constant speed a distance of 5.0m downward along a rough slope that makes an angle of 30with the horizontal. The work done by the force of gravity is:

A. 400 J

B. 200 J

C. 69 J

D. 200 J

E. 400 J

                                                                     ans: D

 

20. A man pulls a sled along a rough horizontal surface by applying a constant force 􀁮 F at an angle θ above the horizontal. In pulling the sled a horizontal distance d, the work done by the man is:

A. Fd

B. Fdcos θ

C. Fdsin θ

D. Fd/ cos θ

E. Fd/ sin θ

                                                                     ans: B

 

21. A man wishes to pull a crate 15m across a rough floor by exerting a force of 100 N. The coefficient of kinetic friction is 0.25. For the man to do the least work, the angle between the force and the horizontal should be:

A. 0

B. 14

C. 43

D. 66

E. 76

                                                                     ans: A

 

22. A particle moves 5m in the positive x direction while being acted upon by a constant force  vector F

= (4Ni + (2 N)ˆj (4 N)ˆk . The work done on the particle by this force is:

A. 20 J

B. 10 J

C. 20 J

D. 30 J

E. is impossible to calculate without knowing other forces

                                                                     ans: A

 

23. A block is attached to the end of an ideal spring and moved from coordinate xi to coordinate xf . The relaxed position is at x = 0. The work done by spring is positive if:

A. xi = 2 cm and xf = 4cm

B. xi = 2 cm and xf = 4cm

C. xi = 2 cm and xf = 4 cm

D. xi = 2 cm and xf = 4 cm

E. xi = 4 cm and xf = 2 cm

                                                                     ans: E

 

 

28. An ideal spring is hung vertically from the ceiling. When a 2.0-kg mass hangs at rest from it the spring is extended 6.0 cm from its relaxed length. A downward external force is now applied to the mass to extend the spring an additional 10 cm. While the spring is being extended by the force, the work done by the spring is:

A. 3.6J

B. 3.3J

C. 3.4 × 105 J

D. 3.3J

E. 3.6J

                                                                     ans: A

 

29. An ideal spring is hung vertically from the ceiling. When a 2.0-kg block hangs at rest from it the spring is extended 6.0 cm from its relaxed length. A upward external force is then applied to the block to move it upward a distance of 16 cm. While the block is moving upward the work done by the spring is:

A. 1.0J

B. 0.52 J

C. 0.26 J

D. 0.52 J

E. 1.0J

                                                                     ans: A

 

 

30. Which of the following bodies has the largest kinetic energy?

A. Mass 3M and speed V

B. Mass 3M and speed 2V

C. Mass 2M and speed 3V

D. Mass M and speed 4V

E. All four of the above have the same kinetic energy

                                                                     ans: C

 

31. Two trailers, X with mass 500 kg and Y with mass 2000 kg, are being pulled at the same speed.

The ratio of the kinetic energy of Y to that of X is:

A. 1:1

B. 2:1

C. 4:1

D. 9:1

E. 1500:1

                                                                     ans: C

32. A 8000-N car is traveling at 12m/s along a horizontal road when the brakes are applied. The

car skids to a stop in 4.0 s. How much kinetic energy does the car lose in this time?

A. 4.8 × 104 J

B. 5.9 × 104 J

C. 1.2 × 105 J

D. 5.8 × 105 J

E. 4.8 × 106 J

                                                                                                                                          ans: B

 

33. The velocity of a particle moving along the x axis changes from vi to vf . For which values of

vi and vf is the total work done on the particle positive?

A. vi = 5m/s, vf = 2m/s

B. vi = 5m/s, vf = 2m/s

C. vi = 5m/s, vf = 2m/s

D. vi = 5m/s, vf = 2m/s

E. vi = 2m/s, vf = 5m/s

                                                                     ans: E

 

34. An object is constrained by a cord to move in a circular path of radius 0.5m on a horizontal

frictionless surface. The cord will break if its tension exceeds 16 N. The maximum kinetic

energy the object can have is:

A. 4 J

B. 8 J

C. 16 J

D. 32 J

E. 64 J

                                                                     ans: A

 

35. The weight of an object on the moon is one-sixth of its weight on Earth. The ratio of the

kinetic energy of a body on Earth moving with speed V to that of the same body moving with

speed V on the moon is:

A. 6:1

B. 36:1

C. 1:1

D. 1:6

E. 1:36

                                                                     ans: C

 

36. Which of the following is the correct combination of dimensions for energy?

A. MLT

B. LT2/m

C. ML2/T2

D. M2L3T

E. ML/T2

                                                                     ans: C

 

37. The amount of work required to stop a moving object is equal to:

A. the velocity of the object

B. the kinetic energy of the object

C. the mass of the object times its acceleration

D. the mass of the object times its velocity

E. the square of the velocity of the object

                                                                     ans: B

 

38. A 5.0-kg cart is moving horizontally at 6.0m/s. In order to change its speed to 10.0m/s, the

net work done on the cart must be:

A. 40 J

B. 90 J

C. 160 J

D. 400 J

E. 550 J

                                                                     ans: C

 

41. A 4-kg cart starts up an incline with a speed of 3m/s and comes to rest 2m up the incline.

The total work done on the car is:

A. 6 J

B. 8 J

C. 12 J

D. 18 J

E. impossible to calculate without more information

                                                                     ans: D

 

42. Two objects with masses of m1 and m2 have the same kinetic energy and are both moving to

the right. The same constant force 􀁮 F is applied to the left to both masses. If m1 = 4m2, the

ratio of the stopping distance of m1 to that of m2 is:

A. 1:4

B. 4:1

C. 1:2

D. 2:1

E. 1:1

                                                                     ans: E

 

43. A Boston Red Sox baseball player catches a ball of mass m that is moving toward him with

speed v. While bringing the ball to rest, his hand moves back a distance d. Assuming constant

deceleration, the horizontal force exerted on the ball by his hand is:

A. mv/d

B. mvd

C. mv2/d

D. 2mv/d

E. mv2/(2d)

                                                                     ans: E

 

44. A 0.50-kg object moves on a horizontal circular track with a radius of 2.5m. An external force

of 3.0N, always tangent to the track, causes the object to speed up as it goes around. If it

starts from rest its speed at the end of one revolution is:

A. 9.8m/s

B. 14m/s

C. 15m/s

D. 19m/s

E. 21m/s

                                                                     ans: B

 

45. A 0.50-kg object moves on a horizontal frictionless circular track with a radius of 2.5m. An

external force of 3.0N, always tangent to the track, causes the object to speed up as it goes

around. If it starts from rest, then at the end of one revolution the radial component of the

force of the track on it is:

A. 19N

B. 38N

C. 47N

D. 75N

E. 96N

                                                                     ans: B

 

46. A 2-kg block is attached to a horizontal ideal spring with a spring constant of 200N/m. When

the spring has its equilibrium length the block is given a speed of 5m/s. What is the maximum

elongation of the spring?

A. 0

B. 0.05m

C. 5m

D. 10m

E. 100m

                                                                     ans: C

 

47. At time t = 0 a particle starts moving along the x axis. If its kinetic energy increases uniformly

with t the net force acting on it must be:

A. constant

B. proportional to t

C. inversely proportional to t

D. proportional to t

E. proportional to 1/t

                                                                     ans: E

 

50. A 1.5-kg crate falls from a height of 2.0m onto an industrial spring scale with a spring constant

of 1.5 × 105 N/m. At its greatest compression the reading on the scale is:

A. 15N

B. 30N

C. 1.5 × 103 N

D. 2.1 × 103 N

E. 3.0 × 103 N

                                                                     ans: E

 

 

 

53. In raising an object to a given height by means of an inclined plane, as compared with raising

the object vertically, there is a reduction in:

A. work required

B. distance pushed

C. friction

D. force required

E. value of the acceleration due to gravity

                                                                     ans: D

 

54. A watt is:

A. kg · m/s3

B. kg · m2/s

C. kg · m2/s3

D. kg · m/s

E. kg · m2/s2

                                                                     ans: C

 

55. Power has the dimensions of:

A. ML2/T2

B. MT/L2

C. ML/T2

D. ML2/T3

E. none of these

                                                                     ans: D

 

56. Which of the following five units represents a quantity that is NOT the same as the other four?

A. joule

B. erg

C. watt

D. foot·pound

E. newton·meter

                                                                     ans: C

 

57. Which of the following five quantities is NOT an expression for energy? Here m is a mass,

g is the acceleration due to gravity, h and d are distances, F is a force, v is a speed, a is an

acceleration, P is power, and t is time.

A. mgh

B. Fd

C. 1/2mv2

D. ma

E. Pt

                                                                     ans: D

58. A watt·second is a unit of:

A. force

B. power

C. displacement

D. speed

E. energy

                                                                     ans: E

 

59. A watt per hour is a unit of:

A. energy

B. power

C. force

D. acceleration

E. none of these

                                                                     ans: E

60. A kilowatt·hour is a unit of:

A. power

B. energy/time

C. work

D. power/time

E. force/distance

                                                                     ans: C

62. A woman lifts a barbell 2.0m in 5.0 s. If she lifts it the same distance in 10 s, the work done

by her is:

A. four times as great

B. two times as great

C. the same

D. half as great

E. one-fourth as great

                                                                     ans: C

 

64. A person holds an 80-N weight 2m above the floor for 30 seconds. The power required to do

this is:

A. 80W

B. 40W

C. 20W

D. 10W

E. none of these

                                                                     ans: E

 

65. A 50-N force is the only force on a 2-kg object that starts from rest. When the force has been

acting for 2 s the rate at which it is doing work is:

A. 75W

B. 100W

C. 1000W

D. 2500W

E. 5000W

                                                                     ans: D

 

66. A 50-N force is the only force a 2-kg crate that starts from rest. At the instant the object has

gone 2m the rate at which the force is doing work is:

A. 2.5W

B. 25W

C. 75W

D. 100W

E. 500W

                                                                     ans: E

 

67. A particle starts from rest and is acted on by a net force that does work at a rate that is proportional to the time t. The speed of the particle is proportional to:

A. t

B. t

C. t2

D. 1/t

E. 1/t

                                                                     ans: A

 

 

 

 

Chapter 8: POTENTIAL ENERGY AND CONSERVATION OF ENERGY

 

1. Only if a force on a particle is conservative:

A. is its work zero when the particle moves exactly once around any closed path

B. is its work always equal to the change in the kinetic energy of the particle

C. does it obey Newton’s second law

D. does it obey Newton’s third law

E. is it not a frictional force

                                                                     ans: A

 

2. A nonconservative force:

A. violates Newton’s second law

B. violates Newton’s third law

C. cannot do any work

D. must be perpendicular to the velocity of the particle on which it acts

E. none of the above

                                                                     ans: E

 

3. The sum of the kinetic and potential energies of a system of objects is conserved:

A. only when no external force acts on the objects

B. only when the objects move along closed paths

C. only when the work done by the resultant external force is zero

D. always

E. none of the above

                                                                     ans: E

 

4. A force on a particle is conservative if:

A. its work equals the change in the kinetic energy of the particle

B. it obeys Newton’s second law

C. it obeys Newton’s third law

D. its work depends on the end points of every motion, not on the path between

E. it is not a frictional force

                                                                     ans: D

 

5. Two particles interact by conservative forces. In addition, an external force acts on each particle. They complete round trips, ending at the points where they started. Which of the following must have the same values at the beginning and end of this trip?

A. the total kinetic energy of the two-particle system

B. the potential energy of the two-particle system

C. the mechanical energy of the two-particle system

D. the total linear momentum of the two-particle system

E. none of the above

                                                                     ans: B

 

6. Two objects interact with each other and with no other objects. Initially object A has a speed of 5m/s and object B has a speed of 10m/s. In the course of their motion they return to their initial positions. Then A has a speed of 4m/s and B has a speed of 7m/s. We can conclude:

A. the potential energy changed from the beginning to the end of the trip

B. mechanical energy was increased by nonconservative forces

C. mechanical energy was decreased by nonconservative forces

D. mechanical energy was increased by conservative forces

E. mechanical energy was decreased by conservative forces

                                                                     ans: C

 

7. A good example of kinetic energy is provided by:

A. a wound clock spring

B. the raised weights of a grandfather’s clock

C. a tornado

D. a gallon of gasoline

E. an automobile storage battery

                                                                     ans: C

 

8. No kinetic energy is possessed by:

A. a shooting star

B. a rotating propeller on a moving airplane

C. a pendulum at the bottom of its swing

D. an elevator standing at the fifth floor

E. a cyclone

                                                                     ans: D

 

9. The wound spring of a clock possesses:

A. kinetic but no potential energy

B. potential but no kinetic energy

C. both potential and kinetic energy in equal amounts

D. neither potential nor kinetic energy

E. both potential and kinetic energy, but more kinetic energy than potential energy

                                                                     ans: B

 

10. A body at rest in a system is capable of doing work if:

A. the potential energy of the system is positive

B. the potential energy of the system is negative

C. it is free to move in such a way as to decrease its kinetic energy

D. it is free to move in such a way as to decrease the potential energy of the system

E. it is free to move in such a way as to increase the potential energy of the system

                                                                     ans: D

 

11. Which one of the following five quantities CANNOT be used as a unit of potential energy?

A. watt·second

B. gram·cm/s2

C. joule

D. kg·m2/s2

E. ft·lb

                                                                     ans: B

 

12. Suppose that the fundamental dimensions are taken to be: force (F), velocity (V) and time (T). The dimensions of potential energy are then:

A. F/T

B. FVT

C. FV/T

D. F/T2

E. FV2/T2

                                                                     ans: B

 

14. A golf ball is struck by a golf club and falls on a green three meters above the tee. The potential

energy of the Earth-ball system is greatest:

A. just before the ball is struck

B. just after the ball is struck

C. just after the ball lands on the green

D. when the ball comes to rest on the green

E. when the ball reaches the highest point in its flight

                                                                     ans: E

 

16. A 6.0-kg block is released from rest 80m above the ground. When it has fallen 60m its kinetic

energy is approximately:

A. 4800 J

B. 3500 J

C. 1200 J

D. 120 J

E. 60 J

                                                                     ans: B

 

17. A 2-kg block is thrown upward from a point 20m above Earth’s surface. At what height above Earth’s surface will the gravitational potential energy of the Earth-block system have increased by 500 J?

A. 5m

B. 25m

C. 46m

D. 70m

E. 270m

                                                                     ans: C

 

18. An elevator is rising at constant speed. Consider the following statements:

I. the upward cable force is constant

II. the kinetic energy of the elevator is constant

III. the gravitational potential energy of the Earth-elevator system is constant

IV. the acceleration of the elevator is zero

V. the mechanical energy of the Earth-elevator system is constant

A. all five are true

B. only II and V are true

C. only IV and V are true

D. only I, II, and III are true

E. only I, II, and IV are true

                                                                     ans: E

 

19. A projectile of mass 0.50 kg is fired with an initial speed of 10m/s at an angle of 60above the horizontal. The potential energy of the projectile-Earth system (relative potential energy when the projectile is at ground level) is:

A. 25 J

B. 18.75 J

C. 12.5J

D. 6.25 J

E. none of these

                                                                     ans: B

 

21. A 2.2-kg block starts from rest on a rough inclined plane that makes an angle of 25with the horizontal. The coefficient of kinetic friction is 0.25. As the block goes 2.0m down the plane the mechanical energy of the Earth-block system changes by:

A. 0

B. 9.8J

C. 9.8J

D. 18 J

E. 18 J

                                                                     ans: B

 

24. A particle moves along the x axis under the influence of a stationary object. The net force on the particle is given by F = (8N/m3)x3. If the potential energy is taken to be zero for x = 0 then the potential energy is given by:

A. (2 J/m4)x4

B. (2J/m4)x4

C. (24 J/m2x2

D. (24 J/m2)x2

E. 5 J (2 J/m4)x4

                                                                     ans: B

 

25. A 0.20-kg particle moves along the x axis under the influence of a stationary object. The potential energy is given by U(x) = (8.0J/m2)x2 + (2.0J/m4)x4 ,

where x is in coordinate of the particle. If the particle has a speed of 5.0m/s when it is at

x = 1.0m, its speed when it is at the origin is:

A. 0

B. 2.5m/s

C. 5.7m/s

D. 7.9m/s

E. 11m/s

                                                                     ans: E

 

27. A force of 10N holds an ideal spring with a 20-N/m spring constant in compression. The potential energy stored in the spring is:

A. 0.5J

B. 2.5J

C. 5 J

D. 10 J

E. 200 J

                                                                     ans: B

 

28. An ideal spring is used to fire a 15.0-g pellet horizontally. The spring has a spring constant of 20N/m and is initially compressed by 7.0 cm. The kinetic energy of the pellet as it leaves the spring is:

A. zero

B. 2.5 × 102 J

C. 4.9 × 102 J

D. 9.8 × 102 J

E. 1.4J

                                                                     ans: C

 

29. A 0.50-kg block attached to an ideal spring with a spring constant of 80N/m oscillates on a horizontal frictionless surface. The total mechanical energy is 0.12 J. The greatest extension of the spring from its equilibrium length is:

A. 1.5 × 103 m

B. 3.0 × 103 m

C. 0.039m

D. 0.054m

E. 18m

                                                                     ans: D

 

30. A 0.50-kg block attached to an ideal spring with a spring constant of 80N/m oscillates on a horizontal frictionless surface. The total mechanical energy is 0.12 J. The greatest speed of the block is:

A. 0.15m/s

B. 0.24m/s

C. 0.49m/s

D. 0.69m/s

E. 1.46m/s

                                                                     ans: D

 

31. A 0.50-kg block attached to an ideal spring with a spring constant of 80N/m oscillates on a horizontal frictionless surface. When the spring is 4.0 cm longer than its equilibrium length, the speed of the block is 0.50m/s. The greatest speed of the block is:

A. 0.23m/s

B. 0.32m/s

C. 0.55m/s

D. 0.71m/s

E. 0.93m/s

                                                                     ans: D

 

32. A 0.5-kg block slides along a horizontal frictionless surface at 2m/s. It is brought to rest by compressing a very long spring of spring constant 800N/m. The maximum spring compression is:

A. 0

B. 3 cm

C. 5 cm

D. 80 cm

E. 80m

                                                                     ans: C

 

 

34. A 700-N man jumps out of a window into a fire net 10m below. The net stretches 2m before bringing the man to rest and tossing him back into the air. The maximum potential energy of the net, compared to its unstretched potential energy, is:

A. 300 J

B. 710 J

C. 850 J

D. 7000 J

E. 8400 J

                                                                     ans: E

 

60. A 5-kg projectile is fired over level ground with a velocity of 200m/s at an angle of 25above the horizontal. Just before it hits the ground its speed is 150m/s. Over the entire trip the change in the internal energy of the projectile and air is:

A. +19, 000 J

B. 19, 000 J

C. +44, 000 J

D. 44, 000 J

E. 0

                                                                     ans: C

 

61. A 0.75-kg block slides on a rough horizontal table top. Just before it hits a horizontal idea spring its speed is 3.5m/s. It compresses the spring 5.7 cm before coming to rest. If the spring constant is 1200N/m, the internal energy of the block and the table top must have:

A. not changed

B. decreased by 1.9J

C. decreased by 2.6J

D. increased by 1.9J

E. increased by 2.6J

                                                                     ans: C

 

 

 

 

Chapter 9: CENTER OF MASS AND LINEAR MOMENTUM

 

1. Which one of the following statements is true?

A. the center of mass of an object must lie within the object

B. all the mass of an object is actually concentrated at its center of mass

C. the center of mass of an object cannot move if there is zero net force on the object

D. the center of mass of a cylinder must lie on its axis

E. none of the above

                                                                     ans: E

 

3. The center of mass of a uniform disk of radius R is located:

A. on the rim

B. a distance R/2 from the center

C. a distance R/3 from the center

D. a distance 2R/3 from the center

E. at the center

                                                                     ans: E

 

4. The center of mass of the system consisting of Earth, the Sun, and the planet Mars is:

A. closer to Earth than to either of the other bodies

B. closer to the Sun than to either of the other bodies

C. closer to Mars than to either of the other bodies

D. at the geometric center of the triangle formed by the three bodies

E. at the center of the line joining Earth and Mars

                                                                     ans: B

 

5. The center of mass of Earth’s atmosphere is:

A. a little less than halfway between Earth’s surface and the outer boundary of the atmosphere

B. near the surface of Earth

C. near the outer boundary of the atmosphere

D. near the center of Earth

E. none of the above

                                                                     ans: D

 

 

 

8. Block A, with a mass of 4 kg, is moving with a speed of 2.0m/s while block B, with a mass of 8 kg, is moving in the opposite direction with a speed of 3m/s. The center of mass of the two block-system is moving with a velocity of:

A. 1.3m/s in the same direction as A

B. 1.3m/s in the same direction as B

C. 2.7m/s in the same direction as A

D. 1.0m/s in the same direction as B

E. 5.0m/s in the same direction as A

                                                                     ans: B

 

9. At the same instant that a 0.50-kg ball is dropped from 25m above Earth, a second ball, with a mass of 0.25 kg, is thrown straight upward from Earth’s surface with an initial speed of 15m/s. They move along nearby lines and pass each other without colliding. At the end of 2.0 s the height above Earth’s surface of the center of mass of the two-ball system is:

A. 2.9m

B. 4.0m

C. 5.0m

D. 7.1m

E. 10.4m

                                                                     ans: D

 

16. A man sits in the back of a canoe in still water. He then moves to the front of the canoe and

sits there. Afterwards the canoe:

A. is forward of its original position and moving forward

B. is forward of its original position and moving backward

C. is rearward of its original position and moving forward

D. is rearward of its original position and moving backward

E. is rearward of its original position and not moving

                                                                     ans: E

 

21. A 2.0-kg block is attached to one end of a spring with a spring constant of 100N/m and a

4.0-kg block is attached to the other end. The blocks are placed on a horizontal frictionless

surface and set into motion. At one instant the 2.0-kg block is observed to be traveling to the

right with a speed of 0.50m/s and the 4.0-kg block is observed to be traveling to the left with

a speed of 0.30m/s. Since the only forces on the blocks are the force of gravity, the normal

force of the surface, and the force of the spring, we conclude that:

A. the spring is compressed at the time of the observation

B. the spring is not compressed at the time of observation

C. the motion was started with the masses at rest

D. the motion was started with at least one of masses moving

E. the motion was started by compressing the spring

                                                                     ans: D

 

22. A 2.0-kg mass is attached to one end of a spring with a spring constant of 100N/m and a 4.0-kg mass is attached to the other end. The masses are placed on a horizontal frictionless surface and the spring is compressed 10 cm. The spring is then released with the masses at rest and the masses oscillate. When the spring has its equilibrium length for the first time the 2.0-kg mass has a speed of 0.36m/s. The mechanical energy that has been lost to the instant is:

A. zero

B. 0.31 J

C. 0.61 J

D. 0.81 J

E. 1.2J

                                                                     ans: B

 

23. Momentum may be expressed in:

A. kg/m

B. gram·s

C. N·s

D. kg/(m·s)

E. N/s

                                                                     ans: C

 

24. The momentum of an object at a given instant is independent of its:

A. inertia

B. mass

C. speed

D. velocity

E. acceleration

                                                                     ans: E

 

25. Two bodies, A and B, have equal kinetic energies. The mass of A is nine times that of B. The

ratio of the momentum of A to that of B is:

A. 1:9

B. 1:3

C. 1:1

D. 3:1

E. 9:1

                                                                     ans: D

 

26. Two objects, P and Q, have the same momentum. Q has more kinetic energy than P if it:

A. weighs more than P

B. is moving faster than P

C. weighs the same as P

D. is moving slower than P

E. is moving at the same speed as P

                                                                     ans: B

 

27. A particle moves along the x axis. Its momentum is graphed below as a function of time. Rank

the numbered regions according to the magnitude of the force acting on the particle, least to

greatest.

 

 

 

28. A 1.0-kg ball moving at 2.0m/s perpendicular to a wall rebounds from the wall at 1.5m/s.

The change in the momentum of the ball is:

A. zero

B. 0.5N · s away from wall

C. 0.5N · s toward wall

D. 3.5N · s away from wall

E. 3.5N · s toward wall

                                                                     ans: D

 

29. If the total momentum of a system is changing:

A. particles of the system must be exerting forces on each other

B. the system must be under the influence of gravity

C. the center of mass must have constant velocity

D. a net external force must be acting on the system

E. none of the above

                                                                     ans: D

 

30. When you step on the accelerator to increase the speed of your car, the force that accelerates

the car is:

A. the force of your foot on the accelerator

B. the force of friction of the road on the tires

C. the force of the engine on the drive shaft

D. the normal force of the road on the tires

E. none of the above

                                                                     ans: B

 

31. A 2.5-kg stone is released from rest and falls toward Earth. After 4.0 s, the magnitude of its

momentum is:

A. 98 kg · m/s

B. 78 kg · m/s

C. 39 kg · m/s

D. 24 kg · m/s

E. zero

                                                                     ans: A

 

32. A 64-kg woman stands on frictionless level ice with a 0.10-kg stone at her feet. She kicks the

stone with her foot so that she acquires a velocity of 0.0017m/s in the forward direction. The

velocity acquired by the stone is:

A. 1.1m/s forward

B. 1.1m/s backward

C. 0.0017m/s forward

D. 0.0017m/s backward

E. none of these

                                                                     ans: B

 

33. A man is marooned at rest on level frictionless ice. In desperation, he hurls his shoe to the

right at 15m/s. If the man weighs 720N and the shoe weighs 4.0N, the man moves to the left

with a speed of:

A. 0

B. 2.1 × 102 m/s

C. 8.3 × 102 m/s

D. 15m/s

E. 2.7 × 103 m/s

                                                                     ans: C

 

34. Two spacemen are floating together with zero speed in a gravity-free region of space. The mass

of spaceman A is 120 kg and that of spaceman B is 90 kg. Spaceman A pushes B away from

him with B attaining a final speed of 0.5m/s. The final recoil speed of A is:

A. zero

B. 0.38m/s

C. 0.5m/s

D. 0.67m/s

E. 1.0m/s

                                                                     ans: B

 

35. A projectile in flight explodes into several fragments. The total momentum of the fragments

immediately after this explosion:

A. is the same as the momentum of the projectile immediately before the explosion

B. has been changed into kinetic energy of the fragments

C. is less than the momentum of the projectile immediately before the explosion

D. is more than the momentum of the projectile immediately before the explosion

E. has been changed into radiant energy

                                                                     ans: A

 

36. A rifle of mass M is initially at rest but free to recoil. It fires a bullet of mass m and velocity

v (relative to the ground). After firing, the velocity of the rifle (relative to the ground) is:

A. mv

B. Mv/m

C. mv/M

D. v

E. mv/M

                                                                     ans: C

 

37. Bullets from two revolvers are fired with the same velocity. The bullet from gun #1 is twice as

heavy as the bullet from gun #2. Gun #1 weighs three times as much as gun #2. The ratio

of the momentum imparted to gun #1 to that imparted to gun #2 is:

A. 2:3

B. 3:2

C. 2:1

D. 3:1

E. 6:1

                                                                     ans: C

 

 

39. Force:

A. equals the negative integral (with respect to distance) of the potential energy function

B. is the ability to do work

C. is the rate of change of doing work

D. equals the time rate of change of momentum

E. has dimensions of momentum multiplied by time

                                                                     ans: D

 

40. Cart A, with a mass of 0.20 kg, travels on a horizontal air track at 3.0m/s and hits cart B,

which has a mass of 0.40 kg and is initially traveling away from A at 2.0m/s. After the collision

the center of mass of the two cart system has a speed of:

A. zero

B. 0.33m/s

C. 2.3m/s

D. 2.5m/s

E. 5.0m/s

                                                                     ans: B

 

42. A cart loaded with sand slides forward along a horizontal frictionless track. As the cart moves,

sand trickles out at a constant rate through a hole in the back of the cart. The acceleration of

the cart is:

A. constant and in the forward direction

B. constant and in the backward direction

C. variable and in the forward direction

D. variable and in the backward direction

E. zero

                                                                     ans: E

47. The physical quantity “impulse” has the same dimensions as that of:

A. force

B. power

C. energy

D. momentum

E. work

                                                                     ans: D

 

48. The law of conservation of momentum applies to a system of colliding objects only if:

A. there is no change in kinetic energy of the system

B. the coefficient of restitution is one

C. the coefficient of restitution is zero

D. the net external impulse is zero

E. the collisions are all elastic

                                                                     ans: D

 

49. Sphere X, of mass 2 kg, is moving to the right at 10m/s. Sphere Y, of mass 4 kg, is moving to

the left at 10m/s. The two spheres collide head-on. The magnitude of the impulse of X on Y

is:

A. twice the magnitude of the impulse of Y on X

B. half the magnitude of the impulse of Y on X

C. one-fourth the magnitude of the impulse of Y on X

D. four times the magnitude of the impulse of Y on X

E. the same as the magnitude of the impulse of Y on X

                                                                     ans: E

 

50. Two bodies of unequal mass, placed at rest on a frictionless surface, are acted on by equal

horizontal forces for equal times. Just after these forces are removed, the body of greater mass

will have:

A. the greater speed

B. the greater acceleration

C. the smaller momentum

D. the greater momentum

E. the same momentum as the other body

                                                                     ans: E

 

51. A 0.2-kg rubber ball is dropped from the window of a building. It strikes the sidewalk below

at 30m/s and rebounds up at 20m/s. The impulse on the ball during the collision is:

A. 10N · s upward

B. 10N · s downward

C. 2.0N · s upward

D. 2.0N · s downward

E. 9.8N · s upward

                                                                     ans: A

 

52. A 10-kg block of ice is at rest on a frictionless horizontal surface. A 1.0-N force is applied in

an easterly direction for 1.0 s. During this time interval, the block:

A. acquires a speed of 1m/s

B. moves 10 cm

C. acquires a momentum of 1.0kg · m/s

D. acquires a kinetic energy of 0.1J

E. none of the above

                                                                     ans: C

 

54. What magnitude impulse will give a 2.0-kg object a momentum change of magnitude + 50 kg · m/s?

A. +25N · s

B. 25N · s

C. +50N · s

D. 50N · s

E. +100N · s

                                                                     ans: C

 

55. A student’s life was saved in an automobile accident because an airbag expanded in front of

his head. If the car had not been equipped with an airbag, the windshield would have stopped

the motion of his head in a much shorter time. Compared to the windshield, the airbag:

A. causes a much smaller change in momentum

B. exerts a much smaller impulse

C. causes a much smaller change in kinetic energy

D. exerts a much smaller force

E. does much more work

                                                                     ans: D

 

59. Whenever an object strikes a stationary object of equal mass:

A. the two objects cannot stick together

B. the collision must be elastic

C. the first object must stop

D. momentum is not necessarily conserved

E. none of the above

                                                                     ans: E

 

60. For a two-body collision involving objects with different masses, a frame of reference which has

the same velocity relative to the laboratory as does the center of mass of the two objects is:

A. a frame for which the momentum of the incident object is zero

B. a frame for which the momentum of the target object is zero

C. a frame for which the average momentum of the two objects is zero

D. a frame for which the total momentum of the two objects is zero

E. none of the above

                                                                     ans: D

 

61. An inelastic collision is one in which:

A. momentum is not conserved but kinetic energy is conserved

B. total mass is not conserved but momentum is conserved

C. neither kinetic energy nor momentum is conserved

D. momentum is conserved but kinetic energy is not conserved

E. the total impulse is equal to the change in kinetic energy

                                                                     ans: D

62. A 4.0-N puck is traveling at 3.0m/s. It strikes a 8.0-N puck, which is stationary. The two

pucks stick together. Their common final speed is:

A. 1.0m/s

B. 1.5m/s

C. 2.0m/s

D. 2.3m/s

E. 3.0m/s

                                                                     ans: A

 

63. A 3.00-g bullet traveling horizontally at 400m/s hits a 3.00-kg wooden block, which is initially

at rest on a smooth horizontal table. The bullet buries itself in the block without passing

through. The speed of the block after the collision is:

A. 1.33m/s

B. 0.40m/s

C. 12.0m/s

D. 40.0m/s

E. 160m/s

                                                                     ans: B

 

64. A 2-kg cart, traveling on a horizontal air track with a speed of 3m/s, collides with a stationary

4-kg cart. The carts stick together. The impulse exerted by one cart on the other has a

magnitude of:

A. 0

B. 4N · s

C. 6N · s

D. 9N · s

E. 12N · s

                                                                     ans: B

 

65. A 3-g bullet is fired horizontally into a 10-kg block of wood suspended by a rope from the

ceiling. The block swings in an arc, rising 3mm above its lowest position. The velocity of the

bullet was:

A. unknown since the heat generated in the collision was not given

B. 8.0 × 102 m/s

C. 24.0m/s

D. 8.00m/s

E. 2.4 × 104 m/s

                                                                     ans: B

 

66. A 3.0-kg and a 2.0-kg cart approach each other on a horizontal air track. They collide and

stick together. After the collision their total kinetic energy is 40 J. The speed of their center

of mass is:

A. zero

B. 2.8m/s

C. 4.0m/s

D. 5.2m/s

E. 6.3m/s

                                                                     ans: C

 

67. Blocks A and B are moving toward each other. A has a mass of 2.0 kg and a velocity of 50m/s,

while B has a mass of 4.0 kg and a velocity of 25m/s. They suffer a completely inelastic

collision. The kinetic energy lost during the collision is:

A. 0

B. 1250 J

C. 3750 J

D. 5000 J

E. 5600 J

                                                                     ans: C

 

68. For a completely inelastic two-body collision the kinetic energy retained by the objects is the

same as:

A. the total kinetic energy before the collision

B. the difference in the kinetic energies of the objects before the collision

C. 1

2Mv2

com, where M is the total mass and vcom is the velocity of the center of mass

D. the kinetic energy of the more massive body before the collision

E. the kinetic energy of the less massive body before the collision

                                                                     ans: C

 

69. A 75-kg man is riding in a 30-kg cart at 2.0m/s. He jumps off in such a way as to land on the

ground with no horizontal velocity. The resulting change in speed of the cart is:

A. zero

B. 2.0m/s

C. 3.0m/s

D. 5.0m/s

E. 7.0m/s

                                                                     ans: D

 

70. An elastic collision is one in which:

A. momentum is not conserved but kinetic energy is conserved

B. total mass is not conserved but momentum is conserved

C. kinetic energy and momentum are both conserved

D. momentum is conserved but kinetic energy is not conserved

E. the total impulse is equal to the change in kinetic energy

                                                                     ans: C

 

71. Object A strikes the stationary object B head-on in an elastic collision. The mass of A is fixed,

you may choose the mass of B appropriately. Then:

A. for B to have the greatest recoil speed, choose mB = mA

B. for B to have the greatest recoil momentum, choose mB 􀁕 mA

C. for B to have the greatest recoil kinetic energy, choose mB 􀁕 mA

D. for B to have the least recoil speed, choose mB = mA

E. for B to have the greatest recoil kinetic energy, choose mB = mA

                                                                     ans: E

 

72. Block A, with a mass of 2.0 kg, moves along the x axis with a velocity of 5.0m/s in the positive

x direction. It suffers an elastic collision with block B, initially at rest, and the blocks leave the

collision along the x axis. If B is much more massive than A, the speed of A after the collision

is:

A. 0

B. +5.0m/s

C. 5.0m/s

D. +10m/s

E. 10m/s

                                                                     ans: C

 

73. A very massive object traveling at 10m/s strikes a very light object, initially at rest, and the

light object moves off in the direction of travel of the heavy object. If the collision is elastic,

the speed of the lighter object is:

A. 5.0m/s

B. 10m/s

C. 15m/s

D. 20m/s

E. Can’t tell from the information given.

                                                                     ans: D

 

74. Sphere A has mass m and is moving with velocity v. It makes a head-on elastic collision with

a stationary sphere B of mass 2m. After the collision their speeds (vA and vB) are:

A. 0, v/2

B. v/3, 2v/3

C. v, v

D. 2v/3, v/3

E. none of these

                                                                     ans: B

 

75. Blocks A and B are moving toward each other along the x axis. A has a mass of 2.0 kg and

a velocity of 50m/s, while B has a mass of 4.0 kg and a velocity of 25m/s. They suffer an

elastic collision and move off along the x axis. The kinetic energy transferred from A to B

during the collision is:

A. 0

B. 2500 J

C. 5000 J

D. 7500 J

E. 10000 J

                                                                     ans: A

 

76. When a particle suffers a head-on elastic collision with another particle, initially at rest, the

greatest fraction of kinetic energy is transferred if:

A. the incident particle is initially traveling very fast

B. the incident particle is traveling very slowly

C. the incident particle is much more massive than the target particle

D. the incident particle is much less massive than the target particle

E. the incident and target particle have the same mass

                                                                     ans: E

 

77. Two objects, X and Y, are held at rest on a horizontal frictionless surface and a spring is

compressed between them. The mass of X is 2/5 times the mass of Y. Immediately after the

spring is released, X has a kinetic energy of 50 J and Y has a kinetic energy of:

A. 20 J

B. 8 J

C. 310 J

D. 125 J

E. 50 J

                                                                     ans: D

 

79. Two identical carts travel at 1m/s in opposite directions on a common horizontal surface. They

collide head-on and are reported to rebound, each with a speed of 2m/s. Then:

A. momentum was not conserved; therefore, the report must be false

B. if some other form of energy were changed to kinetic during the collision, the report could

be true

C. if the collision were elastic, the report could be true

D. if friction were present, the report could be true

E. if the duration of the collision were long enough, the report could be true

                                                                     ans: B

 

80. A block moves at 5.0m/s in the positive x direction and hits an identical block, initially at

rest. A small amount of gunpowder had been placed on one of the blocks. The explosion does

not harm the blocks but it doubles their total kinetic energy. After the explosion the blocks

move along the x axis and the incident block has a speed in of:

A. 1.8m/s

B. 5.0m/s

C. 6.8m/s

D. 7.1m/s

E. 11.8m/s

                                                                     ans: A