Chapter
10 Chapter Resources
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Section
10.1
Chapter Resources
Energy and Work
● Work is the transfer of energy by mechanical
means.
● A moving object has kinetic energy.
Section
10.1
Chapter Resources
Energy and Work
● The work done on a system is equal to the
change in energy of the system.
● Work is the product of the force exerted on an
object and the distance the object moves in
the direction of the force.
Section
10.1
Chapter Resources
Energy and Work
● The work done can be determined by
calculating the area under a forcedisplacement graph.
● Power is the rate of doing work, that is
the rate at which energy is transferred.
Section
10.2
Chapter Resources
Machines
● Machines, whether powered by engines or
humans, do not change the amount of work
done, but they do make the task easier.
● A machine eases the load, either by changing
the magnitude or the direction of the force
exerted to do work.
Section
10.2
Chapter Resources
Machines
● The mechanical advantage, MA, is the ratio of
resistance force to effort force.
● The ideal mechanical advantage, IMA, is the
ratio of the distances moved.
Section
10.2
Chapter Resources
Machines
● The efficiency of a machine is the ratio of
output work to input work.
Section
10.2
Chapter Resources
Machines
● In all real machines, MA is less than IMA.
● The efficiency of a machine can be found
from the real and ideal mechanical
advantages.
Chapter
10 Chapter Resources
Chapter Assessment
Questions
1. Juan pulled a crate with a rope angled 25° above the
horizontal, applying a constant force of 40 N over a
distance of 100 m. Find the work performed by Juan.
A. (40 N) (100 m)
B. (40 N) (100 m) sin 25°
C. (40 N) (100 m) cos 25°
D. (40 N) (100 m) tan 25°
Chapter
10 Chapter Resources
Chapter Assessment
Questions
Reason: When force is applied at an angle, work is
equal to the product of force and
displacement times the cosine of the angle
between the force and the direction of the
displacement.
That is,
W = Fd cos  = (40 N) (100 m) cos 25°
Chapter
10 Chapter Resources
Chapter Assessment
Questions
2. Three motors, A, B, and C were tested to lift
water from a tank to the top of a building. The
results are as follows.
Motor A of mass 1.0 kg lifted the water in 120 s.
Motor B of mass 1.5 kg lifted the same amount of
water in 135 s. Motor C of mass 2.0 kg lifted the
same amount of water in 150 s.
Which of the motors produced the most power?
Chapter
10 Chapter Resources
Chapter Assessment
Questions
A. Motor A
B. Motor B
C. Motor C
D. All three motors produce the same power.
Chapter
10 Chapter Resources
Chapter Assessment
Questions
Reason: Power is equal to the work done,
divided by the time taken to do work
(P = W/t).
Since all three motors are doing the
same work, the motor doing the work
in the least time (that is, Motor A)
produces the most power.
Chapter
10 Chapter Resources
Chapter Assessment
Questions
3. While riding a multi-speed bicycle, the muscles in Jack’s
body exert a constant force of 400 N. If he covers a
distance of 200 m in 1 minute, what is the power
delivered by Jack?
A.
C.
B.
D.
Chapter
10 Chapter Resources
Chapter Assessment
Questions
Reason: Power is equal to the work done,
divided by the time taken to do work.
Since W = Fd,
Chapter
10 Chapter Resources
Chapter Assessment
Questions
4. John is pushing a huge
table in his house. As John
pushes the table farther
and farther, he applies
more and more force. A
graph of force (N) applied
by John versus the
displacement (m) of the
table is given. What work
does John do on the table?
Chapter
10 Chapter Resources
Chapter Assessment
Questions
A. (45 N)(3.0 m)
B. -(45 N)(3.0 m)
C.
D.
Chapter
10 Chapter Resources
Chapter Assessment
Questions
Reason: The area under the force-displacement graph
is equal to the work done by that force, even if
the force changes. Therefore, the work done
by John in pushing the table is the area of a
triangle:
Chapter
10 Chapter Resources
Chapter Assessment
Questions
5. Explain why the output work of a simple machine can
never be greater than the input work.
Answer: A simple machine is not a source of energy. It
only transfers the energy supplied to it. Therefore, the
substance to which a machine transfers energy cannot
receive more energy than the amount of energy put into
it. Hence, the output work of a simple machine can
never be greater than the input work.
Chapter
10 Chapter Resources
Chapter Assessment
Questions
6. If the efficiency of a machine is 100%, what can you
say about the mechanical advantage and the ideal
mechanical advantage of the machine?
A. The mechanical advantage is greater than the ideal
mechanical advantage.
B. The mechanical advantage is equal to the ideal
mechanical advantage.
C. The ideal mechanical advantage is greater than the
mechanical advantage.
D. The mechanical advantage of the machine is zero.
Chapter
10 Chapter Resources
Chapter Assessment
Questions
Reason: The efficiency of a machine (in percent) is
equal to its mechanical advantage, divided
by the ideal mechanical advantage,
multiplied by 100%.
Hence, if the efficiency of a machine is
100%, MA = IMA. That is, mechanical
advantage is equal to the ideal mechanical
advantage.
Chapter
10 Chapter Resources
Standardized Test Practice
1. A pulley system consists of two fixed pulleys and two
movable pulleys that lift a load that has a weight of 300 N.
If the effort force used to lift the load is 100 N, what is the
mechanical advantage of the system?
A.
C. 3
B.
D. 6
Chapter
10 Chapter Resources
Standardized Test Practice
2. The box in the diagram is
being pushed up the ramp with
a force of 100.0 N. If the height
of the ramp is 3.0 m, what is
the work done on the box?
(sin 30° = 0.50, cos 30° = 0.87,
tan 30° = 0.58)
A. 150 J
C. 450 J
B. 260 J
D. 600 J
Chapter
10 Chapter Resources
Standardized Test Practice
3. A compound machine used to raise heavy boxes
consists of a ramp and a pulley. The efficiency of
pulling a 100-kg box up the ramp is 50%. If the
efficiency of the pulley is 90%, what is the overall
efficiency of the compound machine?
A. 40%
B. 45%
C. 50%
D. 70%
Chapter
10 Chapter Resources
Standardized Test Practice
4. A skater with a mass of 50.0 kg slides across an icy
pond with negligible friction. As he approaches a friend,
both he and his friend hold out their hands, and the
friend exerts a force in the direction opposite to the
skater’s movement, which lowers the skater’s speed
from 2.0 m/s to 1.0 m/s. What is the change in the
skater’s kinetic energy?
A. 25 J
C. 100 J
B. 75 J
D. 150 J
Chapter
10 Chapter Resources
Standardized Test Practice
5. A 20.0-N block is attached to the end of a rope, and the
rope is looped around a pulley system. If you pull the
opposite end of the rope a distance of 2.00 m, the pulley
system raises the block a distance of 0.40 m. What is
the pulley system’s ideal mechanical advantage?
A. 2.5
B. 4.0
C. 5.0
D. 10.0
Chapter
10 Chapter Resources
Standardized Test Practice
6. Two people carry identical 40.0-N boxes up a ramp. The
ramp is 2.00 m long and rests on a platform that is 1.00 m
high. One person walks up the ramp in 2.00 s, and the
other person walks up the ramp in 4.00 s. What is the
difference in power the two people use to carry the boxes
up the ramp?
A. 5.00 W
C. 20.0 W
B. 10.0 W
D. 40.0 W
Chapter
10 Chapter Resources
Standardized Test Practice
7. A 4-N soccer ball sits motionless on a field. A player’s
foot exerts a force of 5 N on the ball for a distance of
0.1 m, and the ball rolls a distance of 10 m. How much
kinetic energy does the ball gain from the player?
A. 0.5 J
B. 0.9 J
C. 9 J
D. 50 J
Chapter
10 Chapter Resources
Standardized Test Practice
8. The diagram shows a box being pulled by a rope with
a force of 200.0 N along a horizontal surface. The
angle the rope makes with the horizontal is 45°.
Calculate the work done on the box and the power
required to pull it a distance of 5.0 m in 10.0 s.
(sin 45° = cos 45° = 0.7)
Chapter
10 Chapter Resources
Standardized Test Practice
Answer:
Chapter
10 Chapter Resources
Standardized Test Practice
Test-Taking Tip
Beat the Clock and then Go Back
As you take a practice test, pace yourself to finish
each section just a few minutes early so you can
go back and check over your work.
Chapter
10 Chapter Resources
Physics: Principles and Problems Transparencies
Chapter
10 Chapter Resources
Image Bank
Chapter
10 Chapter Resources
Image Bank
Chapter
10 Chapter Resources
Image Bank
Chapter
10 Chapter Resources
A 100-g Mass on a Flat Surface
Attached to a Spring Scale
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Chapter
10 Chapter Resources
A Constant Force Exerted on the
Backpack
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Chapter
10 Chapter Resources
Motion of the Planet Around the Sun
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Chapter
10 Chapter Resources
A Man Pushing a Car
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Chapter
10 Chapter Resources
Constant Force Exerted at an Angle
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Chapter
10 Chapter Resources
Work Diagram
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Chapter
10 Chapter Resources
Work and Energy
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Chapter
10 Chapter Resources
Force and Displacement at an Angle
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Chapter
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Bicycle Rider Pushing a Bicycle
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Chapter
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Work Done by a Force
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Chapter
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Work Done by a Force
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Chapter
10 Chapter Resources
Three Students Climbing the Stairs at
Different Rates
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Chapter
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Power
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Chapter
10 Chapter Resources
A Winch Designed to be Mounted on
a Truck
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Chapter
10 Chapter Resources
Maximizing Power on a Multi-speed
Bicycle
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Chapter
10 Chapter Resources
A Bottle Opener as an Example of a
Simple Machine
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Chapter
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A Pulley System
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Chapter
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An Electric Pump
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Chapter
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Examples of Simple Machines
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Chapter
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A Steering Wheel
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Chapter
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A Bicycle
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Chapter
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Mechanical Advantage
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Chapter
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Mechanical Advantage
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Chapter
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A Pulley System
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Chapter
10 Chapter Resources
The Human Walking Machine
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Chapter
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A Flight of Stairs
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Chapter
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Bicycle Gear Shifters
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Chapter
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A Claw Hammer
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Chapter
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A Lawn Tractor
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Chapter
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A Sled Being Pulled by Diego
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Chapter
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A Crate Being Pushed Up an Inclined
Ramp
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Chapter
10 Chapter Resources
The Magnitude of the Force
Necessary to Stretch a Spring
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Chapter
10 Chapter Resources
A Crate Being Pushed Up an Inclined
Plane
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Chapter
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The Force and Displacement of an
Object Being Pulled
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Chapter
10 Chapter Resources
Finding the Real MA and the Efficiency
of a Ramp
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Chapter
10 Chapter Resources
Luisa Pedals a Bicycle with a Gear Radius
of 5.00 cm and a Wheel Radius of 38.6 cm
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Chapter
10 Chapter Resources
Power v. Mass
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Chapter
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A Box Being Pushed Up the Ramp
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Chapter
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A Box Being Pulled By a Rope
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Chapter
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Section 10.1 Vocabulary
work
energy
kinetic energy
work-energy theorem
joule
power
watt
Chapter
10 Chapter Resources
Section 10.2 Vocabulary
machine
efficiency
effort force
compound machine
resistance force
mechanical advantage
ideal mechanical
advantage
Chapter
10 Chapter Resources
Work and Energy
Calculating Work
Calculating Work by Constant Force Acting on
an Angle
Power
Benefits of Machines
Chapter
10 Chapter Resources
Mechanical Advantage (1)
Mechanical Advantage (2)