Revision for midsemester 2
Multiple Choice
Identify the choice that best completes the statement or answers the question.
____
1. In which of the following sentences is work used in the scientific sense of the word?
a. Holding a heavy box requires a lot of work.
b. A scientist works on an experiment in the laboratory.
c. Sam and Rachel pushed hard, but they could do no work on the car.
d. John learned that shoveling snow is hard work.
____
2. In which of the following sentences is work used in the everyday sense of the word?
a. Lifting a heavy bucket involves doing work on the bucket.
b. The force of friction usually does negative work.
c. Sam and Rachel worked hard pushing the car.
d. Work is a physical quantity.
____
3. A force does work on an object if a component of the force
a. is perpendicular to the displacement of the object.
b. is parallel to the displacement of the object.
c. perpendicular to the displacement of the object moves the object along a path that returns
the object to its starting position.
d. parallel to the displacement of the object moves the object along a path that returns the
object to its starting position.
____
4. Work is done when
a. the displacement is not zero.
b. the displacement is zero.
c. the force is zero.
d. the force and displacement are perpendicular.
____
5. What is the common formula for work? Assume that W is the work, F is a constant force, v is the change in
velocity, and d is the displacement.
a. W = Fv
c. W = Fd
b. W = Fd
d. W = F d
____
6. If the sign of work is negative,
a. the displacement is perpendicular to the force.
b. the displacement is in the direction opposite the force.
c. the displacement is in the same direction as the force.
d. no work is done.
____
7. In which of the following scenarios is work done?
a. A weightlifter holds a barbell overhead for 2.5 s.
b. A construction worker carries a heavy beam while walking at constant speed along a flat
surface.
c. A car decelerates while traveling on a flat stretch of road.
d. A student holds a spring in a compressed position.
____
8. In which of the following scenarios is no net work done?
a. A car accelerates down a hill.
b. A car travels at constant speed on a flat road.
c. A car decelerates on a flat road.
d. A car decelerates as it travels up a hill.
____
9. A child moving at constant velocity carries a 2 N ice-cream cone 1 m across a level surface. What is the net
work done on the ice-cream cone?
a. 0 J
c. 2 J
b. 0.5 J
d. 20 J
____ 10. A worker does 25 J of work lifting a bucket, then sets the bucket back down in the same place. What is the
total net work done on the bucket?
a. –25 J
c. 25 J
b. 0 J
d. 50 J
____ 11. A construction worker pushes a wheelbarrow 5.0 m with a horizontal force of 50.0 N. How much work is
done by the worker on the wheelbarrow?
a. 10 J
c. 250 J
b. 55 J
d. 1250 J
____ 12. A horizontal force of 200 N is applied to move a 55 kg television set across a 10 m level surface. What is the
work done by the 200 N force on the television set?
a. 550 J
c. 6000 J
b. 2000 J
d. 11000 J
____ 13. A child pulls a balloon for 12 m with a force of 1.0 N at an angle 60 below horizontal. How much work does
the child do on the balloon?
a. –10 J
c. 6.0 J
b. –6.0 J
d. 12 J
____ 14. Which of the following energy forms is associated with an object in motion?
a. potential energy
c. nonmechanical energy
b. elastic potential energy
d. kinetic energy
____ 15. Which of the following energy forms is associated with an object due to its position?
a. potential energy
c. total energy
b. positional energy
d. kinetic energy
____ 16. Which of the following energy forms is not involved in hitting a tennis ball?
a. kinetic energy
c. gravitational potential energy
b. chemical potential energy
d. elastic potential energy
____ 17. Which of the following formulas would be used to directly calculate the kinetic energy of an object with mass
m bouncing up and down on a spring with spring constant k?
a.
c.
b.
d.
____ 18. Ball A has triple the mass and speed of ball B. What is the ratio of the kinetic energy of ball A to ball B.
a. 3
c. 9
b. 6
d. 27
____ 19. What is the kinetic energy of a 0.135 kg baseball thrown at 40.0 m/s?
a. 54.0 J
c. 108 J
b. 87.0 J
d. 216 J
____ 20. Which of the following equations expresses the work-kinetic energy theorem?
a.
c.
b.
d.
____ 21. If friction is the only force acting on an object during a given physical process, which of the following
assumptions can be made in regard to the object’s kinetic energy?
a. The kinetic energy decreases.
b. The kinetic energy increases.
c. The kinetic energy remains constant.
d. The kinetic energy decreases and then increases.
____ 22. The main difference between kinetic energy and potential energy is that
a. kinetic energy involves position, and potential energy involves motion.
b. kinetic energy involves motion, and potential energy involves position.
c. although both energies involve motion, only kinetic energy involves position.
d. although both energies involve position, only potential energy involves motion.
____ 23. Which form of energy is involved in weighing fruit on a spring scale?
a. kinetic energy
c. gravitational potential energy
b. nonmechanical energy
d. elastic potential energy
____ 24. Gravitational potential energy is always measured in relation to
a. kinetic energy.
c. total potential energy.
b. mechanical energy.
d. a zero level.
____ 25. The equation for determining gravitational potential energy is PE = mgh. Which factor(s) in this equation is
(are) not intrinsic to an object?
a. m
b. g
c. h
d. both g and h
____ 26. Which of the following parameters does not depend on how resistant a spring is to being compressed or
stretched?
a. compression distance
c. spring constant
b. relaxed length
d. stretching distance
____ 27. What are the units for a spring constant?
a. N
b. m
c. Nm
d. N/m
____ 28. If the displacement of a horizontal mass-spring system was doubled, the elastic potential energy in the system
would change by a factor of
a. 1/4.
c. 2.
b. 1/2.
d. 4.
____ 29. If the mass in a horizontal mass-spring system was doubled, the elastic potential energy in the system would
change by a factor of
a. 0 (no change).
c. 2.
b. 1/2.
d. 4.
____ 30. What is the potential energy of a 1.0 kg mass 1.0 m above the ground?
a. 1.0 J
c. 10 J
b. 9.8 J
d. 96 J
____ 31. How much elastic potential energy is stored in a bungee cord with a spring constant of 10.0 N/m when the
cord is stretched 2.00 m?
a. 10.0 J
c. 40.0 J
b. 20.0 J
d. 200 J
____ 32. Which of the following is a true statement about the conservation of energy?
a. Potential energy is always conserved.
b. Kinetic energy is always conserved.
c. Mechanical energy is always conserved.
d. Total energy is always conserved.
____ 33. In the presence of frictional force,
a. nonmechanical energy is negligible and mechanical energy is no longer conserved.
b. nonmechanical energy is negligible and mechanical energy is conserved.
c. nonmechanical energy is no longer negligible and mechanical energy is conserved.
d. nonmechanical energy is no longer negligible and mechanical energy is no longer
conserved.
____ 34. Why doesn’t the principle of mechanical energy conservation hold in situations when frictional forces are
present?
a. Kinetic energy is not completely converted to a form of potential energy.
b. Potential energy is completely converted to a form of gravitational energy.
c. Chemical energy is not completely converted to electrical energy.
d. Kinetic energy is completely converted to a form of gravitational energy.
____ 35. For which of the following situations is the conservation of mechanical energy most likely to be a valid
assumption?
a. A skateboard rolls across a sewer grate.
b. A parachutist falls from a plane.
c. You rub your hands together to keep warm.
d. A soccer ball flies through the air.
____ 36. Which of the following refers to the sum of kinetic energy and all forms of potential energy?
a. total energy
c. nonmechanical energy
b.  energy
d. mechanical energy
____ 37. Which of the following are examples of conservable quantities?
a. potential energy and length
c. mechanical energy and mass
b. mechanical energy and length
d. kinetic energy and mass
____ 38. Which of the following is a form of mechanical energy?
a. internal energy
c. gravitational potential energy
b. chemical potential energy
d. electrical energy
____ 39. Friction converts kinetic energy to
a. mechanical energy.
b. potential energy.
c. nonmechanical energy.
d. total energy.
____ 40. A 3.00 kg toy falls from a height of 1.00 m. What will the kinetic energy of the toy be just before the toy hits
the ground? (Assume no air resistance and that g = 9.81 m/s .)
a. 0.98 J
c. 29.4 J
b. 9.8 J
d. 294 J
____ 41. Which of the following is the rate at which energy is transferred?
a. potential energy
c. mechanical energy
b. kinetic energy
d. power
____ 42. Which of the following is the rate at which work is done?
a. potential energy
c. mechanical energy
b. kinetic energy
d. power
____ 43. Which of the following equations is not an equation for power, P, in terms of work, W, displacement, d, time
interval, t, force, F, and/or velocity, v?
a.
c.
b.
d.
____ 44. Which of the following are not units of power?
a. hp
c. W
b. J
d. Js
____ 45. How much power is required to lift a 2.0 kg mass at a speed of 2.0 m/s?
a. 2.0 J
c. 9.8 J
b. 4.0 J
d. 39 J
____ 46. What is the average power supplied by a 60.0 kg person running up a flight of stairs a vertical distance of 4.0
m in 4.2 s?
a. 57 W
c. 560 W
b. 240 W
d. 670 W
____ 47. Which of the following has the greatest power output?
a. a weightlifter who lifts a 250 N weight 2.1 m in 3.0 s
b. a mechanic’s lift that raises a 1.2  10 N car 2.1 m in 12 s
c. a car engine that does 1.2  10 J of work in 5.0 s
d. a crane that lifts a 2.5  10 N beam at a speed of 1.2 m/s
____ 48. A more powerful motor can do
a. more work in a longer time interval.
b. the same work in a shorter time interval.
c. less work in a longer time interval.
d. the same work in a longer time interval.
____ 49. Which of the following equations can be used to directly calculate an object’s momentum, p?
a. p = mv
c. p = Ft
b.
d. p = Ft
____ 50. What are the SI units for momentum?
a. Nm
b. J
c. kgm/s
d. kgm/s
____ 51. When comparing the momentum of two moving objects, which of the following is correct?
a.
b.
c.
d.
The object with the higher velocity will have less momentum if the masses are equal.
The more massive object will have less momentum if its velocity is greater.
The less massive object will have less momentum if the velocities are the same.
The more massive object will have less momentum if the velocities are the same.
____ 52. A child with a mass of 23 kg rides a bike with a mass of 5.5 kg at a velocity of 4.5 m/s to the south. Compare
the momentum of the child with the momentum of the bike.
a. Both the child and the bike have the same momentum.
b. The bike has a greater momentum than the child.
c. The child has a greater momentum than the bike.
d. Neither the child nor the bike has momentum.
____ 53. Which of the following has the greatest momentum?
a. a tortoise with a mass of 275 kg moving at a velocity of 0.55 m/s
b. a hare with a mass of 2.7 kg moving at a velocity of 7.5 m/s
c. a turtle with a mass of 91 kg moving at a velocity of 1.4 m/s
d. a roadrunner with a mass of 1.8 kg moving at a velocity of 6.7 m/s
____ 54. A roller coaster climbs up a hill at 4 m/s and then zips down the hill at 30 m/s. The momentum of the roller
coaster
a. is greater up the hill than down the hill.
b. is greater down the hill than up the hill.
c. remains the same throughout the ride.
d. is zero throughout the ride.
____ 55. A person sitting in a chair with wheels stands up, causing the chair to roll backward across the floor. The
momentum of the chair
a. was zero while stationary and increased when the person stood.
b. was greatest while the person sat in the chair.
c. remained the same.
d. was zero when the person got out of the chair and increased while the person sat.
____ 56. A rubber ball moving at a speed of 5 m/s hit a flat wall and returned to the thrower at 5 m/s. The magnitude of
the momentum of the rubber ball
a. increased.
c. remained the same.
b. decreased.
d. was not conserved.
____ 57. Which of the following equations can be used to directly calculate the change in an object’s momentum?
a. p = mv
c. p = Ft
b.
d. p = Ft
____ 58. If a force is exerted on an object, which statement is true?
a. A large force always produces a large change in the object’s momentum.
b. A large force produces a large change in the object’s momentum only if the force is
applied over a very short time interval.
c. A small force applied over a long time interval can produce a large change in the object’s
momentum.
d. A small force always produces a large change in the object’s momentum.
____ 59. The change in an object’s momentum is equal to
a. the product of the mass of the object and the time interval.
b. the product of the force applied to the object and the time interval.
c. the time interval divided by the net external force.
d. the net external force divided by the time interval.
____ 60. Which of the following situations is an example of a visible change in momentum?
a. A hiker walks through a spider’s web.
c. A volleyball hits a mosquito in the air.
b. A car drives over a pebble.
d. A baseball is hit by a bat.
____ 61. Which of the following situations is an example of a significant change in momentum?
a. A tennis ball is hit into a net.
b. A helium-filled balloon rises upward into the sky.
c. An airplane flies into some scattered white clouds.
d. A bicyclist rides over a leaf on the pavement.
____ 62. A ball with a momentum of 4.0 kgm/s hits a wall and bounces straight back without losing any kinetic
energy. What is the change in the ball’s momentum?
a. –8.0 kgm/s
c. 0.0 kgm/s
b. –4.0 kgm/s
d. 8.0 kgm/s
____ 63. A 0.2 kg baseball is pitched with a velocity of 40 m/s and is then batted to the pitcher with a velocity of 60
m/s. What is the magnitude of change in the ball’s momentum?
a. 2 kgm/s
c. 8 kgm/s
b. 4 kgm/s
d. 20 kgm/s
____ 64. The impulse experienced by a body is equivalent to the body’s change in
a. velocity.
c. momentum.
b. kinetic energy.
d. force.
____ 65. Which of the following statements properly relates the variables in the equation Ft = p?
a. A large constant force changes an object’s momentum over a long time interval.
b. A large constant force acting over a long time interval causes a large change in
momentum.
c. A large constant force changes an object’s momentum at various time intervals.
d. A large constant force does not necessarily cause a change in an object’s momentum.
____ 66. A 75 kg person walking around a corner bumped into an 80 kg person who was running around the same
corner. The momentum of the 80 kg person
a. increased.
c. remained the same.
b. decreased.
d. was conserved.
____ 67. A 20 kg shopping cart moving at a velocity of 0.5 m/s collides with a store wall and stops. The momentum of
the shopping cart
a. increases.
c. remains the same.
b. decreases.
d. is conserved.
____ 68. A soccer ball collides with another soccer ball at rest. The total momentum of the balls
a. is zero.
c. remains constant.
b. increases.
d. decreases.
____ 69. Two skaters stand facing each other. One skater’s mass is 60 kg, and the other’s mass is 72 kg. If the skaters
push away from each other without spinning,
a. the lighter skater has less momentum.
b. their momenta are equal but opposite.
c. their total momentum doubles.
d. their total momentum decreases.
____ 70. In a two-body collision,
a. momentum is always conserved.
b. kinetic energy is always conserved.
c. neither momentum nor kinetic energy is conserved.
d. both momentum and kinetic energy are always conserved.
____ 71. The law of conservation of momentum states that
a. the total initial momentum of all objects interacting with one another usually equals the
total final momentum.
b. the total initial momentum of all objects interacting with one another does not equal the
total final momentum.
c. the total momentum of all objects interacting with one another is zero.
d. the total momentum of all objects interacting with one another remains constant regardless
of the nature of the forces between the objects.
____ 72. Which of the following statements about the conservation of momentum is not correct?
a. Momentum is conserved for a system of objects pushing away from each other.
b. Momentum is not conserved for a system of objects in a head-on collision.
c. Momentum is conserved when two or more interacting objects push away from each other.
d. The total momentum of a system of interacting objects remains constant regardless of
forces between the objects.
Short Answer
73. Explain the scientific meaning of work.
74. In the following sentence, is the everyday meaning or the scientific meaning of work intended?
A student works on a term paper.
75. In the following sentence, is the everyday meaning or the scientific meaning of work intended?
A coach does work on the bleachers by moving them into place before the basketball game.
76. In the following sentence, is the everyday meaning or the scientific meaning of work intended?
A bulldozer does work lifting a load.
77. In the following sentence, is the everyday meaning or the scientific meaning of work intended?
A clerk works overtime on Saturdays.
78. How is work related to force and displacement?
79. What formula can be used to calculate work if the force acts at an angle to the displacement?
80. Name the two SI units for work.
81. Is work a vector quantity or a scalar quantity?
82. A child pulls a toy across the floor. Is the work done on the toy positive, negative, or zero?
83. Air exerts a force on a leaf as it falls from a tree to Earth. Is the work done on the leaf positive, negative, or
zero?
A car travels at a speed of 25 m/s on a flat stretch of road. The driver must maintain pressure on the
accelerator to keep the car moving at this speed.
84. Are any forces doing work on the car? Explain your answer.
85. What is the net work done on the car over a distance of 250 m?
86. The car’s engine is doing work on the car, yet the kinetic energy of the car is not changing. What is happening
to the energy supplied by the engine?
87. What form of energy is associated with the position of an object in Earth’s gravitational field?
88. What form of energy is stored in any stretched or compressed object?
89. Is kinetic energy a vector quantity or a scalar quantity?
90. State, in words, the work-kinetic energy theorem.
91. Negative work is done on a moving object. How does the kinetic energy of the object change?
92. Describe the relationship between kinetic energy and gravitational potential energy during the free fall of a
pencil from a desk.
93. A pocket watch contains a long, spiral piece of metal which is coiled tightly as the watch is wound. What
form of potential energy is involved in winding a pocket watch?
94. An object is lowered into a deep hole in the ground. How does the potential energy of the object change?
95. You are analyzing the flight of a projectile through the air. What assumption do you have to make in order to
use conservation of mechanical energy in your analysis?
96. A ski jumper has 1.2  10 J of potential energy at the top of the ski jump. The friction on the jump slope is
small, but not negligible. What can you conclude about the ski jumper’s kinetic energy at the bottom of the
jump? Explain your answer.
97. What quantity is the sum of the kinetic energy and all forms of potential energy in a system?
98. List three different forms of mechanical energy.
99. Write a symbolic expression of the conservation of mechanical energy.
100. Write an equation that expresses the conservation of mechanical energy in a system where the only forms of
mechanical energy are kinetic energy and gravitational potential energy.
101. Write an equation that expresses the conservation of mechanical energy in a system where the only forms of
mechanical energy are kinetic energy and elastic potential energy.
102. Write an equation that expresses the conservation of mechanical energy in a system that involves kinetic
energy, gravitational potential energy, and elastic potential energy.
103. A pendulum is raised 1.5 cm and allowed to fall. If air resistance is negligible, how high will the pendulum
rise on the other side?
104. A child does 5.0 J of work on a spring while loading a ball into a spring-loaded toy gun. If mechanical energy
is conserved, what will be the kinetic energy of the ball when it leaves the gun?
105. Explain how energy, time, and power are related.
106. How are work and power related?
107. Is power a vector quantity or a scalar quantity?
108. Show how the alternative definition of power can be derived by substituting the definitions of work and speed
into the standard definition of power,
.
109. What does the wattage of a light bulb indicate?
110. How is a machine’s power rating related to its rate of doing work on an object?
111. In terms of energy, what occurs when a machine does work on an object?
112. Which motor performs more work in the same amount of time—a 10 kW motor or a 20 kW motor? How
much more work can it do?
113. What is the kinetic energy of a 1.5  10 kg car traveling at 25 m/s?
114. Write the equation for momentum, first using symbols for the variables, then using words for the variables.
115. As a bullet travels through the air, it slows down due to air resistance. How does the bullet’s momentum
change as a result?
116. An ice skater initially skating at a velocity of 3 m/s speeds up to a velocity of 5 m/s. How does the momentum
of the skater change?
117. A student walks to class at a velocity of 3 m/s. To avoid walking into a door as it opens, the student slows to a
velocity of 0.5 m/s. Now late for class, the student runs down the corridor at a velocity of 7 m/s. At what point
in this scenario does the student have the least momentum?
118. A baseball pitcher’s first pitch is a fastball, moving at high speed. The pitcher’s second pitch—with the same
ball—is a changeup, moving more slowly. Which pitch is harder for the catcher to stop? Explain your answer
in terms of momentum.
119. Is it possible for a spaceship traveling with constant velocity to experience a change in momentum? Explain
your answer.
120. How can a small force produce a large change in momentum?
121. A force is applied to stop a moving shopping cart. How would increasing the time interval change the force
required?
122. A moderate force will break an egg. Using the concepts of momentum, force, and time interval, explain why
an egg is more likely to break when it is dropped on concrete than if it is dropped on grass.
123. What is a term for the quantity Ft, where F is an applied force and t is the time interval over which the
force is applied?
124. Two pickup trucks are approaching a stop sign. One truck is carrying a load of bricks and has a mass 1.5
times the other truck. Both trucks are initially moving at the same speed. The empty truck comes to a stop in
50.0 m. If the loaded truck uses the same braking force, how much space will the truck need to come to a
complete stop?
125. A large moving ball collides with a small stationary ball. Describe how the momentum of each ball changes.
126. A 0.16 kg cue ball is traveling at 10.0 m/s toward a full rack of 15 billiard balls. What is the magnitude of the
total momentum of the system of 16 balls after the cue ball strikes the rack?
127. State, in words, the law of conservation of momentum for an isolated system.
128. Write, in symbolic form, the equation for the conservation of momentum in a two-body system.
129. On a pool table, a moving cue ball collides with the eight ball, which is at rest. Is it possible for both balls to
be at rest after the collision? Use the law of conservation of momentum to explain your reasoning.
130. Each croquet ball in a set has a mass of 0.50 kg. The green ball travels at 10.5 m/s and strikes a stationary red
ball. If the green ball stops moving, what is the final speed of the red ball after the collision?
131. Two objects move separately after colliding, and both the total momentum and total kinetic energy remain
constant. Identify the type of collision.
132. Almost all collisions in the everyday world are of what type?
133. Two snowballs are traveling straight toward each other. One snowball has twice the mass of the other, but is
moving at half the speed. The snowballs meet head-on in a perfectly inelastic collision. What is the total
momentum of the system containing the two snowballs before the collision?
134. Describe how the collision affects the total momentum and total kinetic energy of the system.
Problem
135. A worker pushes a box with a horizontal force of 40.0 N over a level distance of 4.0 m. If a frictional force of
27 N acts on the box in a direction opposite to that of the worker, what net work is done on the box?
136. A flight attendant pulls a 60.0 N flight bag a distance of 239.0 m along a level airport floor at a constant
speed. A 21.0 N force is exerted on the bag at an angle of 66.0 above the horizontal. How much work is done
on the flight bag?
137. A scale contains a spring with a spring constant of 288 N/m. Placing a mass on the scale causes the spring to
be compressed by 2.89 cm. Calculate the elastic potential energy stored in the spring.
138. A pendulum with a mass of 4.0 kg is released from a height of 2.9 cm above the height of its resting position.
How fast will the pendulum be moving when it passes through the lowest point of its swing?
139. Which has a greater momentum—a truck with a mass of 3530 kg moving at a speed of 21 m/s or a car with a
mass of 1620 kg moving at a speed of 54 m/s?
140. A 5.68  10 kg tennis ball moves at a speed of 13 m/s. The ball is struck by a racket, causing it to rebound
in the opposite direction at a speed of 18 m/s. What is the change in the ball’s momentum?
141. A ball with a mass of 0.70 kg and a speed of 7.0 m/s strikes the side of a large box and bounces straight back
with a speed of 4.0 m/s. What is the change in momentum of the ball?
142. A baseball bat strikes a baseball with a force of 37 N. The bat is in contact with the ball for 0.19 s. What is the
magnitude of the change in momentum of the ball?
143. A 46 kg trapeze artist falls straight down onto a safety net. The trapeze artist’s initial speed as she hits the net
is 9.8 m/s, and the net stretches 1.1 m vertically as she comes to a stop. What average net force does the
trapeze artist experience while the net breaks her fall? How many “g’s” of acceleration does she experience
on average? (1 g = 9.81 m/s )
144. A 56.0 kg diver jumps off a diving platform, rises about 1.0 m above the platform, then falls to the pool. What
is the diver’s momentum at her highest point in the dive?
145. A train with a mass of 2.1 10 kg is moving at 12 m/s when the engineer applies the brakes. If the braking
force is constant at 3.7 10 N, how long does it take the train to stop? How far does the train travel during
this time?
146. A 74.0 kg ice-skater standing on frictionless ice throws a 0.12 kg snowball horizontally at a speed of 27.0
m/s. At what speed does the skater move backward?
147. Two carts with masses of 1.3 kg and 0.49 kg, respectively, are held together by a compressed spring. When
released, the 1.3 kg cart moves to the left with a velocity of 3.1 m/s. What is the velocity of the 0.49 kg cart?
(Disregard the mass of the spring.)
148. A 0.12 kg object makes an elastic head-on collision with a 0.18 kg stationary object. The final velocity of the
0.12 kg object after the collision is 0.048 m/s in the direction opposite its initial movement. The final velocity
of the 0.18 kg object after the collision is 0.19 m/s in the same direction as the object which strikes it. What
was the initial velocity of the 0.12 kg object?
149. A cricket ball with a mass of 0.158 kg moves at a speed of 17 m/s. Then the ball is hit by a bat and rebounds
in the opposite direction at a speed of 18 m/s. What is the change in momentum of the ball?
revision
Answer Section
MULTIPLE CHOICE
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
C
C
B
A
B
B
C
B
A
B
C
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
1
1
1
1
1
1
1
1
1
1
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
I
I
I
I
I
II
I
I
II
II
Given
Solution
PTS: 1
12. ANS: B
DIF: IIIA
OBJ: 5-1.4
DIF: IIIA
OBJ: 5-1.4
Given
Solution
PTS: 1
13. ANS: C
Given
Solution
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
5-1.1
5-1.1
5-1.2
5-1.2
5-1.2
5-1.2
5-1.3
5-1.3
5-1.4
5-1.3
14.
15.
16.
17.
18.
19.
PTS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
1
D
A
B
C
D
C
DIF:
PTS:
PTS:
PTS:
PTS:
PTS:
IIIA
1
1
1
1
1
OBJ:
DIF:
DIF:
DIF:
DIF:
DIF:
5-1.4
I
I
I
I
II
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
5-2.1
5-2.1
5-2.1
5-2.2
5-2.2
DIF:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
IIIA
1
1
1
1
1
1
1
1
1
1
OBJ:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
5-2.2
I
II
I
I
I
II
II
I
II
II
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
5-2.3
5-2.3
5-2.4
5-2.5
5-2.5
5-2.5
5-2.5
5-2.6
5-2.6
5-2.6
Given
Solution
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
PTS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
1
D
A
B
D
D
D
B
D
D
A
B
Given
Solution
PTS: 1
31. ANS: B
Given
DIF: IIIA
OBJ: 5-2.6
Solution
32.
33.
34.
35.
36.
37.
38.
39.
40.
PTS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
1
D
D
A
D
D
C
C
C
C
DIF:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
IIIA
1
1
1
1
1
1
1
1
OBJ:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
5-2.6
I
I
II
II
I
I
I
I
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
5-3.1
5-3.1
5-3.1
5-3.1
5-3.2
5-3.2
5-3.2
5-3.2
DIF:
PTS:
PTS:
PTS:
PTS:
IIIA
1
1
1
1
OBJ:
DIF:
DIF:
DIF:
DIF:
5-3.3
I
I
I
I
OBJ:
OBJ:
OBJ:
OBJ:
5-4.1
5-4.1
5-4.1
5-4.1
Given
Solution
41.
42.
43.
44.
45.
PTS:
ANS:
ANS:
ANS:
ANS:
ANS:
1
D
D
D
B
D
Given
Solution
PTS: 1
46. ANS: C
Given
DIF: IIIA
OBJ: 5-4.2
Solution
PTS: 1
47. ANS: D
DIF: IIIA
OBJ: 5-4.2
DIF: IIIA
PTS: 1
OBJ: 5-4.2
DIF: I
Given
a:
b:
c:
d:
Solution
PTS: 1
48. ANS: B
OBJ: 5-4.3
49.
50.
51.
52.
53.
ANS:
ANS:
ANS:
ANS:
ANS:
A
C
C
C
A
PTS:
PTS:
PTS:
PTS:
1
1
1
1
DIF:
DIF:
DIF:
DIF:
I
I
I
II
OBJ:
OBJ:
OBJ:
OBJ:
6-1.1
6-1.1
6-1.1
6-1.1
DIF:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
IIIA
1
1
1
1
1
1
1
1
OBJ:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
6-1.1
I
I
I
I
I
I
I
I
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
6-1.2
6-1.2
6-1.3
6-1.4
6-1.3
6-1.3
6-1.3
6-1.3
Given
a:
b:
c:
d:
Solution
54.
55.
56.
57.
58.
59.
60.
61.
62.
PTS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
Given
1
B
A
C
D
C
B
D
A
A
Solution
PTS: 1
63. ANS: D
Given
DIF: II
OBJ: 6-1.3
DIF:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
OBJ:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
DIF:
Solution
64.
65.
66.
67.
68.
69.
70.
71.
72.
PTS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
1
C
B
B
B
C
B
A
D
B
IIIA
1
1
1
1
1
1
1
1
1
6-1.3
I
I
II
II
I
II
I
I
I
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
6-1.4
6-1.4
6-2.1
6-2.1
6-2.2
6-2.2
6-2.3
6-2.3
6-2.3
SHORT ANSWER
73. ANS:
Work, in the scientific sense, is the product of the component of a force along the direction of displacement
and the magnitude of the displacement. No work is done unless a force causes some displacement that is not
perpendicular to the force.
PTS: 1
74. ANS:
everyday meaning
DIF: I
OBJ: 5-1.1
PTS: 1
75. ANS:
scientific meaning
DIF: I
OBJ: 5-1.1
PTS: 1
76. ANS:
scientific meaning
DIF: I
OBJ: 5-1.1
PTS: 1
77. ANS:
everyday meaning
DIF: I
OBJ: 5-1.1
DIF: I
OBJ: 5-1.1
PTS: 1
78. ANS:
Work is equal to the magnitude of the component of a force parallel to the displacement of an object
multiplied by the displacement of the object.
PTS: 1
79. ANS:
W = Fdcos
DIF: I
OBJ: 5-1.2
PTS: 1
DIF: I
80. ANS:
newton-meters (Nm) and joules (J)
OBJ: 5-1.2
PTS: 1
DIF: I
81. ANS:
Work is a scalar quantity.
OBJ: 5-1.2
PTS: 1
82. ANS:
positive
DIF: I
OBJ: 5-1.2
PTS: 1
83. ANS:
negative
DIF: II
OBJ: 5-1.3
PTS: 1
DIF: II
OBJ: 5-1.3
84. ANS:
Yes; both the force of the engine and the force of friction are doing work on the car.
PTS: 1
DIF: II
OBJ: 5-1.3
85. ANS:
The net work is zero (because the net force on the car is zero).
PTS: 1
DIF: II
OBJ: 5-1.4
86. ANS:
Energy equal in amount to the energy supplied by the engine is lost from the system due to friction.
PTS: 1
DIF: II
87. ANS:
gravitational potential energy
OBJ: 5-3.2
PTS: 1
DIF: I
88. ANS:
elastic potential energy
OBJ: 5-2.1
PTS: 1
DIF: I
89. ANS:
Kinetic energy is a scalar quantity.
OBJ: 5-2.1
PTS: 1
DIF: I
OBJ: 5-2.2
90. ANS:
The net work done by the net force acting on an object is equal to the change in the kinetic energy of the
object.
PTS: 1
DIF: I
91. ANS:
The kinetic energy will decrease.
OBJ: 5-2.3
PTS: 1
DIF: II
OBJ: 5-2.3
92. ANS:
At the top of the fall, all the energy is gravitational potential energy. During the fall, gravitational potential
energy decreases as it is transformed into kinetic energy. When the pencil reaches the ground, all the energy is
kinetic energy.
PTS: 1
DIF: II
93. ANS:
elastic potential energy
OBJ: 5-2.4
PTS: 1
DIF: II
94. ANS:
The potential energy decreases.
OBJ: 5-2.5
PTS: 1
DIF: II
OBJ: 5-2.6
95. ANS:
You have to assume that air resistance is negligible.
PTS: 1
DIF: II
OBJ: 5-3.1
96. ANS:
It will be less than 1.2  10 J. Because friction is not negligible, mechanical energy is not conserved, and
some mechanical energy will be lost.
PTS: 1
97. ANS:
mechanical energy
DIF: II
OBJ: 5-3.1
PTS: 1
DIF: I
OBJ: 5-3.2
98. ANS:
kinetic energy, gravitational potential energy, elastic potential energy
PTS: 1
99. ANS:
DIF: I
OBJ: 5-3.2
PTS: 1
100. ANS:
DIF: I
OBJ: 5-3.2
PTS: 1
101. ANS:
DIF: I
OBJ: 5-3.2
PTS: 1
102. ANS:
DIF: I
OBJ: 5-3.2
PTS: 1
103. ANS:
1.5 cm
DIF: I
OBJ: 5-3.2
PTS: 1
104. ANS:
5.0 J
DIF: II
OBJ: 5-3.3
PTS: 1
DIF: II
OBJ: 5-3.3
105. ANS:
Power is the rate at which energy is transferred. In other words, power is the energy transferred in a given
time interval.
PTS: 1
DIF: I
OBJ: 5-4.1
106. ANS:
Power measures how much work is done in a given time interval. In other words, power is the rate of work.
PTS: 1
DIF: I
107. ANS:
Power is a scalar quantity.
OBJ: 5-4.1
PTS: 1
108. ANS:
OBJ: 5-4.1
DIF: I
PTS: 1
DIF: II
OBJ: 5-4.1
109. ANS:
The wattage tells the rate at which energy is converted by the bulb.
PTS: 1
DIF: II
OBJ: 5-4.1
110. ANS:
The power rating of a machine indicates the rate at which it does work on an object.
PTS: 1
DIF: I
OBJ: 5-4.3
111. ANS:
When a machine does work on an object, energy is transferred to that object.
PTS: 1
DIF: II
OBJ: 5-4.3
112. ANS:
The 20 kW motor does twice as much work in the same amount of time.
PTS: 1
113. ANS:
4.7  10 J
DIF: II
OBJ: 5-4.3
Given
Solution
PTS: 1
DIF: IIIA
114. ANS:
p = mv
momentum = mass  velocity
OBJ: 5-2.2
PTS: 1
DIF: I
OBJ: 6-1.1
115. ANS:
The bullet’s momentum decreases as its speed decreases.
PTS: 1
DIF: I
116. ANS:
The skater’s momentum increases.
OBJ: 6-1.2
PTS: 1
DIF: I
OBJ: 6-1.2
117. ANS:
The student has the least momentum when dodging the opening door.
PTS: 1
DIF: I
OBJ: 6-1.2
118. ANS:
The first pitch is harder to stop. The first pitch has greater momentum because it has a greater velocity, so the
change in momentum to zero is greater.
PTS: 1
DIF: II
OBJ: 6-1.2
119. ANS:
Yes, a spaceship traveling with constant velocity could experience a change in momentum if its mass
changed, for example, by burning fuel, or if it is acted upon by an outside force.
PTS: 1
120. ANS:
DIF: II
OBJ: 6-1.3
A small force can produce a large change in momentum if the force acts on an object for a long period of
time.
PTS: 1
DIF: II
OBJ: 6-1.4
121. ANS:
Increasing the time interval would reduce the force required.
PTS: 1
DIF: II
OBJ: 6-1.4
122. ANS:
Stopping a falling egg requires changing the momentum of the egg from its value at the time of first impact to
zero. If the egg hits the concrete, the time interval over which this happens is very small, so the force is large.
If the egg lands on grass, the time interval over which the momentum changes is larger, so the force on the
egg is smaller.
PTS: 1
123. ANS:
impulse
DIF: II
OBJ: 6-1.4
PTS: 1
124. ANS:
75.0 m
DIF: I
OBJ: 6-1.4
Given
m =m
m = 1.5m
v =v =v
v =v =0
x = 50.0 m
Solution
The initial and final speeds, as well as the braking force, are the same for each truck. Because truck 2 has a
mass 1.5 times the mass of truck 1, the stopping distance will be 1.5 times greater for truck 2 than for truck 1.
x = 1.5x = (1.5)(50.0 m) = 75.0 m
PTS: 1
DIF: II
OBJ: 6-1.4
125. ANS:
The momentum of the large ball decreases, and the momentum of the small ball increases.
PTS: 1
126. ANS:
1.6 kgm/s
DIF: II
OBJ: 6-2.1
Given
m = 0.16 kg
v = 10.0 m/s
Solution
p = p = m v = (0.16 kg)(10.0 m/s) = 1.6 kgm/s
PTS: 1
DIF: II
OBJ: 6-2.2
127. ANS:
The total momentum of all objects interacting with one another remains constant regardless of the nature of
the forces between the objects.
PTS: 1
128. ANS:
DIF: I
OBJ: 6-2.3
PTS: 1
DIF: I
OBJ: 6-2.3
129. ANS:
No, the final momentum can equal zero only if the initial momentum was zero. Because the cue ball was
moving, its initial momentum was not zero. Therefore, both balls cannot be at rest after the collision.
PTS: 1
130. ANS:
10.5 m/s
DIF: II
OBJ: 6-2.3
PTS: 1
131. ANS:
elastic
DIF: II
OBJ: 6-2.4
PTS: 1
132. ANS:
inelastic
DIF: I
OBJ: 6-3.1
PTS: 1
133. ANS:
zero
DIF: I
OBJ: 6-3.1
PTS: 1
DIF: II
OBJ: 6-1.1
134. ANS:
The total momentum remains zero, while the kinetic energy decreases. In this case, the kinetic energy after
the collision is zero.
PTS: 1
PROBLEM
135. ANS:
52 J
Given
DIF: II
OBJ: 6-3.2
Solution
PTS: 1
136. ANS:
2040 J
DIF: IIIB
OBJ: 5-1.4
DIF: IIIB
OBJ: 5-1.4
DIF: IIIA
OBJ: 5-2.6
Given
Solution
PTS: 1
137. ANS:
0.120 J
Given
Solution
PTS: 1
138. ANS:
0.75 m/s
Given
Solution
PTS: 1
DIF: IIIA
139. ANS:
The car has a greater momentum.
OBJ: 5-3.3
Given
Solution
PTS: 1
140. ANS:
DIF: IIIA
OBJ: 6-1.1
DIF: IIIA
OBJ: 6-1.3
Given
Solution
PTS: 1
141. ANS:
Given
Solution
PTS: 1
142. ANS:
DIF: IIIA
OBJ: 6-1.3
PTS: 1
DIF: IIIA
143. ANS:
2.0  10 N upward; 4.4 g
OBJ: 6-1.4
Given
Solution
Given
Solution
PTS: 1
144. ANS:
0 kgm/s
DIF: IIIC
OBJ: 6-1.4
Solution
The given values are not needed. Because vtop = 0 m/s and p = mv, p at the top = 0 kgm/s.
PTS: 1
145. ANS:
68 s; 4.1  10 m
DIF: II
OBJ: 6-1.2
DIF: IIIC
OBJ: 6-1.4
Given
Solution
PTS: 1
146. ANS:
4.4  10 m/s
Given
Solution
PTS: 1
147. ANS:
8.2 m/s to the right
DIF: IIIB
OBJ: 6-2.4
DIF: IIIB
OBJ: 6-2.4
Given
Solution
PTS: 1
148. ANS:
0.23 m/s forward
Given
Solution
PTS: 1
149. ANS:
DIF: IIIC
OBJ: 6-3.4
DIF: IIIA
OBJ: 6-1.3
Given
Solution
PTS: 1