Cutnell/Johnson
Physics 7th edition
Classroom Response System Questions
Chapter 6 Work and Energy
Interactive Lecture Questions
6.1.1. A block is in contact with a rough surface as shown in the drawing. The block
has a rope attached to one side. Someone pulls the rope with a force , which is
represented by the vector in the drawing. The force is directed at an angle 
with respect to the horizontal direction. The magnitude of is equal to two times
the magnitude of the frictional force, which is designated f. For what value of 
is the net work on the block equal to zero joules?
a) 0
b) 30
c) 45
d) 60
e) Net work will be done in the object for all values of .
6.1.1. A block is in contact with a rough surface as shown in the drawing. The block
has a rope attached to one side. Someone pulls the rope with a force , which is
represented by the vector in the drawing. The force is directed at an angle 
with respect to the horizontal direction. The magnitude of is equal to two times
the magnitude of the frictional force, which is designated f. For what value of 
is the net work on the block equal to zero joules?
a) 0
b) 30
c) 45
d) 60
e) Net work will be done in the object for all values of .
6.1.2. Some children are practicing catching baseballs. The coach tosses the ball into
the air and hits the ball with his bat. The ball travels nearly horizontally, directly
at the short stop who manages to catch the line drive. Did the coach, via the bat,
do any work on the ball as it was hit?
a) No, it travels nearly horizontally, and no work is done.
b) Yes, work was done on the ball because during the time the force acted on the
ball, the bat and ball moved through some distance.
c) No, there was a force acting on the ball, but there was no displacement while the
force was acting.
d) Yes, work was done on the ball because the force of gravity was acting on the ball
while it was being hit.
e) No work was done on the ball because the ball flew even though the force was no
longer acting on it.
6.1.2. Some children are practicing catching baseballs. The coach tosses the ball into
the air and hits the ball with his bat. The ball travels nearly horizontally, directly
at the short stop who manages to catch the line drive. Did the coach, via the bat,
do any work on the ball as it was hit?
a) No, it travels nearly horizontally, and no work is done.
b) Yes, work was done on the ball because during the time the force acted on the
ball, the bat and ball moved through some distance.
c) No, there was a force acting on the ball, but there was no displacement while the
force was acting.
d) Yes, work was done on the ball because the force of gravity was acting on the ball
while it was being hit.
e) No work was done on the ball because the ball flew even though the force was no
longer acting on it.
6.1.3. Kevin is refinishing his rusty wheelbarrow. He moves his
sandpaper back and forth 45 times over a rusty area, each time
moving a total distance of 0.15 m. Kevin pushes the sandpaper
against the surface with a normal force of 1.8 N. The coefficient of
friction for the metal/sandpaper interface is 0.92. How much work is
done by the kinetic frictional force during the sanding process?
a) + 12 J
b)  12 J
c) + 24 J
d)  24 J
e) zero J
6.1.3. Kevin is refinishing his rusty wheelbarrow. He moves his
sandpaper back and forth 45 times over a rusty area, each time
moving a total distance of 0.15 m. Kevin pushes the sandpaper
against the surface with a normal force of 1.8 N. The coefficient of
friction for the metal/sandpaper interface is 0.92. How much work is
done by the kinetic frictional force during the sanding process?
a) + 12 J
b)  12 J
c) + 24 J
d)  24 J
e) zero J
6.2.1. Which one of the following choices represents the largest
kinetic energy?
a) Mars is moving in its orbit around the Sun.
b) A cyclist is racing in the annual Tour de France bicycle race.
c) A leaf falls from a tree.
d) A cheetah runs at its maximum speed to catch a fleeing zebra.
e) An oil tanker sails through the Panama Canal.
6.2.1. Which one of the following choices represents the largest
kinetic energy?
a) Mars is moving in its orbit around the Sun.
b) A cyclist is racing in the annual Tour de France bicycle race.
c) A leaf falls from a tree.
d) A cheetah runs at its maximum speed to catch a fleeing zebra.
e) An oil tanker sails through the Panama Canal.
6.2.2. A high school baseball pitcher can typically throw a ball at 22 m/s.
Professional baseball pitchers can throw the ball with twice that
speed, but few others can. To see why this is the case, determine the
difference in the kinetic energy of a baseball thrown at v m/s and one
thrown at 2v m/s and express the difference as a percentage.
a) 50 %
b) 100 %
c) 200 %
d) 300 %
e) 400 %
6.2.2. A high school baseball pitcher can typically throw a ball at 22 m/s.
Professional baseball pitchers can throw the ball with twice that
speed, but few others can. To see why this is the case, determine the
difference in the kinetic energy of a baseball thrown at v m/s and one
thrown at 2v m/s and express the difference as a percentage.
a) 50 %
b) 100 %
c) 200 %
d) 300 %
e) 400 %
6.3.1. An elevator supported by a single cable descends a shaft at a constant
speed. The only forces acting on the elevator are the tension in the cable
and the gravitational force. Which one of the following statements is
true?
a) The work done by the tension force is zero joules.
b) The net work done by the two forces is zero joules.
c) The work done by the gravitational force is zero joules.
d) The magnitude of the work done by the gravitational force is larger than
that done by the tension force.
e) The magnitude of the work done by the tension force is larger than that
done by the gravitational force.
6.3.1. An elevator supported by a single cable descends a shaft at a constant
speed. The only forces acting on the elevator are the tension in the cable
and the gravitational force. Which one of the following statements is
true?
a) The work done by the tension force is zero joules.
b) The net work done by the two forces is zero joules.
c) The work done by the gravitational force is zero joules.
d) The magnitude of the work done by the gravitational force is larger than
that done by the tension force.
e) The magnitude of the work done by the tension force is larger than that
done by the gravitational force.
6.3.2. Larry’s gravitational potential energy is 1870 J as he sits 2.20 m
above the ground in a sky diving airplane. What is his
gravitational potential energy when be begins to jump from the
airplane at an altitude of 923 m?
a) 3.29  104 J
b) 9.36  102 J
c) 4.22  106 J
d) 1.87  103 J
e) 7.85  105 J
6.3.2. Larry’s gravitational potential energy is 1870 J as he sits 2.20 m
above the ground in a sky diving airplane. What is his
gravitational potential energy when be begins to jump from the
airplane at an altitude of 923 m?
a) 3.29  104 J
b) 9.36  102 J
c) 4.22  106 J
d) 1.87  103 J
e) 7.85  105 J
6.3.3. A mountain climber pulls a supply pack up the side of a mountain
at constant speed. Which one of the following statements concerning
this situation is false?
a) The net work done by all the forces acting on the pack is zero joules.
b) The work done on the pack by the normal force of the mountain is
zero joules.
c) The work done on the pack by gravity is zero joules.
d) The gravitational potential energy of the pack is increasing.
e) The climber does "positive" work in pulling the pack up the mountain.
6.3.3. A mountain climber pulls a supply pack up the side of a mountain
at constant speed. Which one of the following statements concerning
this situation is false?
a) The net work done by all the forces acting on the pack is zero joules.
b) The work done on the pack by the normal force of the mountain is
zero joules.
c) The work done on the pack by gravity is zero joules.
d) The gravitational potential energy of the pack is increasing.
e) The climber does "positive" work in pulling the pack up the mountain.
6.5.1. Two balls of equal size are dropped from the same height from the
roof of a building. One ball has twice the mass of the other. When
the balls reach the ground, how do the kinetic energies of the two
balls compare?
a) The lighter one has one fourth as much kinetic energy as the other
does.
b) The lighter one has one half as much kinetic energy as the other does.
c) The lighter one has the same kinetic energy as the other does.
d) The lighter one has twice as much kinetic energy as the other does.
e) The lighter one has four times as much kinetic energy as the other
does.
6.5.1. Two balls of equal size are dropped from the same height from the
roof of a building. One ball has twice the mass of the other. When
the balls reach the ground, how do the kinetic energies of the two
balls compare?
a) The lighter one has one fourth as much kinetic energy as the other
does.
b) The lighter one has one half as much kinetic energy as the other does.
c) The lighter one has the same kinetic energy as the other does.
d) The lighter one has twice as much kinetic energy as the other does.
e) The lighter one has four times as much kinetic energy as the other
does.
6.5.2. After an ice storm, ice falls from one of the top floors of a 65-story
building. The ice falls freely under the influence of gravity. Which one of
the following statements concerning this situation is true?
a) The kinetic energy of the ice increases by equal amounts for equal distances.
b) The kinetic energy of the ice increases by equal amounts for equal times.
c) The potential energy of the ices decreases by equal amounts for equal times.
d) The total energy of the block increases by equal amounts over equal
distances.
e) As the block falls, the net work done by all of the forces acting on the ice is
zero joules.
6.5.2. After an ice storm, ice falls from one of the top floors of a 65-story
building. The ice falls freely under the influence of gravity. Which one of
the following statements concerning this situation is true?
a) The kinetic energy of the ice increases by equal amounts for equal distances.
b) The kinetic energy of the ice increases by equal amounts for equal times.
c) The potential energy of the ices decreases by equal amounts for equal times.
d) The total energy of the block increases by equal amounts over equal
distances.
e) As the block falls, the net work done by all of the forces acting on the ice is
zero joules.
6.5.3. Determine the amount of work done in firing a 2.0-kg projectile
with an initial speed of 50 m/s. Neglect any effects due to air
resistance.
a) 900 J
b) 1600 J
c) 2500 J
d) 4900 J
e) This cannot be determined without knowing the launch angle.
6.5.3. Determine the amount of work done in firing a 2.0-kg projectile
with an initial speed of 50 m/s. Neglect any effects due to air
resistance.
a) 900 J
b) 1600 J
c) 2500 J
d) 4900 J
e) This cannot be determined without knowing the launch angle.
6.5.4. A roller coaster car travels down a hill and is moving at 18 m/s as it passes
through a section of straight, horizontal track. The car then travels up
another hill that has a maximum height of 15 m. If frictional effects are
ignored, determine whether the car can reach the top of the hill. If it does
reach the top, what is the speed of the car at the top?
a) No, the car doesn’t make it up the hill. It is going too slow.
b) Yes, the car just barely makes it to the top and stops. The final speed is zero
m/s.
c) Yes, the car not only makes it to the top, but it is moving at 5.4 m/s.
d) Yes, the car not only makes it to the top, but it is moving at 9.0
m/s.
e) Yes, the car not only makes it to the top, but it is moving at 18 m/s.
6.5.4. A roller coaster car travels down a hill and is moving at 18 m/s as it passes
through a section of straight, horizontal track. The car then travels up
another hill that has a maximum height of 15 m. If frictional effects are
ignored, determine whether the car can reach the top of the hill. If it does
reach the top, what is the speed of the car at the top?
a) No, the car doesn’t make it up the hill. It is going too slow.
b) Yes, the car just barely makes it to the top and stops. The final speed is zero
m/s.
c) Yes, the car not only makes it to the top, but it is moving at 5.4 m/s.
d) Yes, the car not only makes it to the top, but it is moving at 9.0
m/s.
e) Yes, the car not only makes it to the top, but it is moving at 18 m/s.
6.5.5. You are investigating the safety of a playground slide. You are
interested in finding out what the maximum speed will be of
children sliding on it when the conditions make it very slippery
(assume frictionless). The height of the slide is 2.5 m. What is
that maximum speed of a child if she starts from rest at the top?
a) 1.9 m/s
b) 2.5 m/s
c) 4.9 m/s
d) 7.0 m/s
e) 9.8 m/s
6.5.5. You are investigating the safety of a playground slide. You are
interested in finding out what the maximum speed will be of
children sliding on it when the conditions make it very slippery
(assume frictionless). The height of the slide is 2.5 m. What is
that maximum speed of a child if she starts from rest at the top?
a) 1.9 m/s
b) 2.5 m/s
c) 4.9 m/s
d) 7.0 m/s
e) 9.8 m/s
6.5.6. A quarter is dropped from rest from the fifth floor of a very tall
building. The speed of the quarter is v just before striking the ground.
From what floor would the quarter have to be dropped from rest for
the speed just before striking the ground to be approximately 2v?
Ignore all air resistance effects to determine your answer.
a) 14
b) 25
c) 20
d) 7
e) 10
6.5.6. A quarter is dropped from rest from the fifth floor of a very tall
building. The speed of the quarter is v just before striking the ground.
From what floor would the quarter have to be dropped from rest for
the speed just before striking the ground to be approximately 2v?
Ignore all air resistance effects to determine your answer.
a) 14
b) 25
c) 20
d) 7
e) 10
6.5.7. Two identical balls are thrown from the same height from the roof of a
building. One ball is thrown upward with an initial speed v. The second
ball is thrown downward with the same initial speed v. When the balls
reach the ground, how do the kinetic energies of the two balls compare?
Ignore any air resistance effects.
a) The kinetic energies of the two balls will be the same.
b) The first ball will have twice the kinetic energy as the second ball.
c) The first ball will have one half the kinetic energy as the second ball.
d) The first ball will have four times the kinetic energy as the second ball.
e) The first ball will have three times the kinetic energy as the second ball.
6.5.7. Two identical balls are thrown from the same height from the roof of a
building. One ball is thrown upward with an initial speed v. The second
ball is thrown downward with the same initial speed v. When the balls
reach the ground, how do the kinetic energies of the two balls compare?
Ignore any air resistance effects.
a) The kinetic energies of the two balls will be the same.
b) The first ball will have twice the kinetic energy as the second ball.
c) The first ball will have one half the kinetic energy as the second ball.
d) The first ball will have four times the kinetic energy as the second ball.
e) The first ball will have three times the kinetic energy as the second ball.
6.6.1. A car is being driven along a country road on a dark and rainy night at
a speed of 20 m/s. The section of road is horizontal and straight. The
driver sees that a tree has fallen and covered the road ahead. Panicking,
the driver locks the brakes at a distance of 20 m from the tree. If the
coefficient of friction between the wheels and road is 0.8, determine the
outcome.
a) The car stops 5.5 m before the tree.
b) The car stops just before reaching the tree.
c) As the car crashes into the tree, its speed is 18 m/s.
d) As the car crashes into the tree, its speed is 9.3 m/s.
e) This problem cannot be solved without knowing the mass of the car.
6.6.1. A car is being driven along a country road on a dark and rainy night at
a speed of 20 m/s. The section of road is horizontal and straight. The
driver sees that a tree has fallen and covered the road ahead. Panicking,
the driver locks the brakes at a distance of 20 m from the tree. If the
coefficient of friction between the wheels and road is 0.8, determine the
outcome.
a) The car stops 5.5 m before the tree.
b) The car stops just before reaching the tree.
c) As the car crashes into the tree, its speed is 18 m/s.
d) As the car crashes into the tree, its speed is 9.3 m/s.
e) This problem cannot be solved without knowing the mass of the car.
6.6.2. A rubber ball is dropped from rest from a height h. The ball bounces off the
floor and reaches a height of 2h/3. How can we use the principle of the
conservation of mechanical energy to interpret this observation?
a) During the collision with the floor, the floor did not push hard enough on the ball
for it to reach its original height.
b) Some of the ball’s potential energy was lost in accelerating it toward the floor.
c) The force of the earth’s gravity on the ball prevented it from returning to its
original height.
d) Work was done on the ball by the gravitational force that reduced the ball’s
kinetic energy.
e) Work was done on the ball by non-conservative forces that resulted in the ball
having less total mechanical energy after the bounce.
6.6.2. A rubber ball is dropped from rest from a height h. The ball bounces off the
floor and reaches a height of 2h/3. How can we use the principle of the
conservation of mechanical energy to interpret this observation?
a) During the collision with the floor, the floor did not push hard enough on the ball
for it to reach its original height.
b) Some of the ball’s potential energy was lost in accelerating it toward the floor.
c) The force of the earth’s gravity on the ball prevented it from returning to its
original height.
d) Work was done on the ball by the gravitational force that reduced the ball’s
kinetic energy.
e) Work was done on the ball by non-conservative forces that resulted in the ball
having less total mechanical energy after the bounce.
6.6.3. The Jensens decided to spend their family vacation white water
rafting. During one segment of their trip down a horizontal section of
the river, the raft (total mass = 544 kg) has an initial speed of 6.75
m/s. The raft then drops a vertical distance of 14.0 m, ending with a
final speed of 15.2 m/s. How much work was done on the raft by
non-conservative forces?
a) 12 100 J
b) 18 200 J
c) 24 200 J
d) 36 300 J
e) 48 400 J
6.6.3. The Jensens decided to spend their family vacation white water
rafting. During one segment of their trip down a horizontal section of
the river, the raft (total mass = 544 kg) has an initial speed of 6.75
m/s. The raft then drops a vertical distance of 14.0 m, ending with a
final speed of 15.2 m/s. How much work was done on the raft by
non-conservative forces?
a) 12 100 J
b) 18 200 J
c) 24 200 J
d) 36 300 J
e) 48 400 J
6.7.1. A dam blocks the passage of a river and generates electricity.
Approximately, 57 000 kg of water fall each second through a
height of 19 m. If one half of the gravitational potential energy of
the water were converted to electrical energy, how much power
would be generated?
a) 2.7 × 106 W
b) 5.3 × 106 W
c) 1.1 × 107 W
d) 1.3 × 108 W
e) 2.7 × 108 W
6.7.1. A dam blocks the passage of a river and generates electricity.
Approximately, 57 000 kg of water fall each second through a
height of 19 m. If one half of the gravitational potential energy of
the water were converted to electrical energy, how much power
would be generated?
a) 2.7 × 106 W
b) 5.3 × 106 W
c) 1.1 × 107 W
d) 1.3 × 108 W
e) 2.7 × 108 W
6.7.2. If the amount of energy needed to operate a 100 W light bulb for
one minute were used to launch a 2-kg projectile, what maximum
height could the projectile reach, ignoring any resistive effects?
a) 20 m
b) 50 m
c) 100 m
d) 200 m
e) 300 m
6.7.2. If the amount of energy needed to operate a 100 W light bulb for
one minute were used to launch a 2-kg projectile, what maximum
height could the projectile reach, ignoring any resistive effects?
a) 20 m
b) 50 m
c) 100 m
d) 200 m
e) 300 m
6.7.3. An SUV is accelerated from rest to a speed v in a time interval t.
Neglecting air resistance effects and assuming the engine is
operating at its maximum power rating when accelerating,
determine the time interval for the SUV to accelerate from rest to a
speed 2v.
a) 2t
b) 4t
c) 2.5t
d) 3t
e) 3.5t
6.7.3. An SUV is accelerated from rest to a speed v in a time interval t.
Neglecting air resistance effects and assuming the engine is
operating at its maximum power rating when accelerating,
determine the time interval for the SUV to accelerate from rest to a
speed 2v.
a) 2t
b) 4t
c) 2.5t
d) 3t
e) 3.5t
6.8.1. A 12 500-kg truck is accelerated from rest by a net force that
decreases linearly with distance traveled. The graph shows this
force. Using the information provided and work-energy methods,
determine the approximate speed of the truck when the force is
removed.
a) 8.41 m/s
b) 12.5 m/s
c) 17.7 m/s
d) 25.0 m/s
e) 35.4 m/s
6.8.1. A 12 500-kg truck is accelerated from rest by a net force that
decreases linearly with distance traveled. The graph shows this
force. Using the information provided and work-energy methods,
determine the approximate speed of the truck when the force is
removed.
a) 8.41 m/s
b) 12.5 m/s
c) 17.7 m/s
d) 25.0 m/s
e) 35.4 m/s