Halliday/Resnick/Walker Fundamentals of Physics

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Halliday/Resnick/WalkerFundamentals of Physics

• Classroom Response System Questions

Chapter 7 Kinetic Energy and Work
Interactive Lecture Questions
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7.3.1. 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.
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7.3.1. 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.
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7.3.2. 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
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7.3.2. 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
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7.3.3. Ignoring friction effects, the amount of
energy required to accelerate a car from rest to
a speed v is E. The energy is delivered to the
car by burning gasoline. What additional amount
of energy is required to accelerate the car to a
speed 2v? a) 0.5E b) E c) 2E d) 3E e) 4E
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7.3.3. Ignoring friction effects, the amount of
energy required to accelerate a car from rest to
a speed v is E. The energy is delivered to the
car by burning gasoline. What additional amount
of energy is required to accelerate the car to a
speed 2v? a) 0.5E b) E c) 2E d) 3E e) 4E
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7.5.1. 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
?.
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7.5.1. 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
?.
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7.5.2. 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.
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7.5.2. 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.
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7.5.3. 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
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7.5.3. 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
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7.5.4. 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.
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7.5.4. 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.
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7.5.5. Two wooden blocks are sliding with the
same kinetic energy across a horizontal
frictionless surface. Block A has a mass m and
block B has a mass 2m. At time t 0 s, the
blocks both slide onto a horizontal surface where
the kinetic coefficient of friction between the
blocks and surface is µk. Let xA represent the
distance that block A slides before coming to a
stop and xB the distance that block B slides
before it stops. Which one of the following
expressions concerning these distances is
correct? a) xA xB b) xA 2xB c) xA
0.5xB d) xA 0.25xB e) xA 4xB
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7.5.5. Two wooden blocks are sliding with the
same kinetic energy across a horizontal
frictionless surface. Block A has a mass m and
block B has a mass 2m. At time t 0 s, the
blocks both slide onto a horizontal surface where
the kinetic coefficient of friction between the
blocks and surface is µk. Let xA represent the
distance that block A slides before coming to a
stop and xB the distance that block B slides
before it stops. Which one of the following
expressions concerning these distances is
correct? a) xA xB b) xA 2xB c) xA
0.5xB d) xA 0.25xB e) xA 4xB
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7.6.1. 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.
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7.6.1. 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.
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7.6.2. 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.
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7.6.2. 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.
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7.6.3. 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.
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7.6.3. 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.
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7.6.4. Consider the box in the drawing. We can
slide the box up the frictionless incline from
point A and to point C or we can slide it along
the frictionless horizontal surface from point A
to point B and then lift it to point C. How does
the work done on the box along path A-C,WAC,
compare to the work done on the box along the two
step path A-B-C, WABC? a) WABC is much
greater than WAC. b) WABC is slightly greater
than WAC. c) WABC is much less than WAC. d)
WABC is slight less than WAC. e) The work done
in both cases is the same.
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7.6.4. Consider the box in the drawing. We can
slide the box up the frictionless incline from
point A and to point C or we can slide it along
the frictionless horizontal surface from point A
to point B and then lift it to point C. How does
the work done on the box along path A-C,WAC,
compare to the work done on the box along the two
step path A-B-C, WABC? a) WABC is much
greater than WAC. b) WABC is slightly greater
than WAC. c) WABC is much less than WAC. d)
WABC is slight less than WAC. e) The work done
in both cases is the same.
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7.7.1. Block A has a mass m and block B has a
mass 2m. Block A is pressed against a spring to
compress the spring by a distance x. It is then
released such that the block eventually separates
from the spring and it slides across a surface
where the friction coefficient is µk. The same
process is applied to block B. Which one of the
following statements concerning the distance that
each block slides before stopping is correct? a)
Block A slides one-fourth the distance that
block B slides. b) Block A slides one-half the
distance that block B slides. c) Block A slides
the same distance that block B slides. d) Block
A slides twice the distance that block B
slides. e) Block A slides four times the
distance that block B slides.
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7.7.1. Block A has a mass m and block B has a
mass 2m. Block A is pressed against a spring to
compress the spring by a distance x. It is then
released such that the block eventually separates
from the spring and it slides across a surface
where the friction coefficient is µk. The same
process is applied to block B. Which one of the
following statements concerning the distance that
each block slides before stopping is correct? a)
Block A slides one-fourth the distance that
block B slides. b) Block A slides one-half the
distance that block B slides. c) Block A slides
the same distance that block B slides. d) Block
A slides twice the distance that block B
slides. e) Block A slides four times the
distance that block B slides.
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7.7.2. In designing a spring loaded cannon,
determine the spring constant required to launch
a 2.0 kg ball with an initial speed of 1.2 m/s
from a position where the spring is displaced
0.15 m from its equilibrium position. a) 16
N/m b) 32 N/m c) 64 N/m d) 130 N/m e) 180
N/m
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7.7.2. In designing a spring loaded cannon,
determine the spring constant required to launch
a 2.0 kg ball with an initial speed of 1.2 m/s
from a position where the spring is displaced
0.15 m from its equilibrium position. a) 16
N/m b) 32 N/m c) 64 N/m d) 130 N/m e) 180
N/m
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7.8.1. 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
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7.8.1. 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
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7.8.2. A net force given by
is applied to an object that is
initially at rest. What is the change in the
objects kinetic energy as it moves from x1
0.50 m to x2 2.50 m? a) 14 J b) 17 J c)
21 J d) 24 J e) 28 J
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7.8.2. A net force given by
is applied to an object that is
initially at rest. What is the change in the
objects kinetic energy as it moves from x1
0.50 m to x2 2.50 m? a) 14 J b) 17 J c)
21 J d) 24 J e) 28 J
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7.9.1. 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
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7.9.1. 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
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7.9.2. A television is rated at 450 W. What is
the cost of operating the TV for 5 hours, if the
utility charges 0.085 per kilowatt-hour? a)
0.12 b) 0.19 c) 0.43 d) 0.85 e) 1.91
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7.9.2. A television is rated at 450 W. What is
the cost of operating the TV for 5 hours, if the
utility charges 0.085 per kilowatt-hour? a)
0.12 b) 0.19 c) 0.43 d) 0.85 e) 1.91
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7.9.3. While you sleep, your body is using energy
at a rate of 77 W. How many food calories are
used during an eight hour period? One food
calorie (C) is equal to 4186 joules. a) 66
C b) 240 C c) 530 C d) 710 C e) 1200 C
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7.9.3. While you sleep, your body is using energy
at a rate of 77 W. How many food calories are
used during an eight hour period? One food
calorie (C) is equal to 4186 joules. a) 66
C b) 240 C c) 530 C d) 710 C e) 1200 C