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Skills Worksheet
Concept Review
Section: Simple Machines
1. Name an example of each of the following types of simple machines:
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a. lever
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b. wedge
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c. pulley
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d. wheel and axle
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e. inclined plane
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f. screw
2. Draw the three types of levers, and label the input force, output force, and
fulcrum on each.
First-class lever
Second-class lever
Third-class lever
3. Compare a wedge and a screw with an inclined plane.
4. Describe how an inclined plane increases the force without changing the
amount of work done.
5. Explain how a wheelbarrow is a compound machine.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Science Spectrum
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Work and Energy
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Answer Key
Bellringer Transparencies
Concept Reviews
SECTION: WORK, POWER, AND
MACHINES
SECTION: WORK, POWER, AND
MACHINES
1. d
2. The person exerts a force on the wall,
1. a. Work is a quantity that measures the
and the wall exerts an equal and opposite force on the person. The force
increases to match the increased force
of the person.
SECTION: SIMPLE MACHINES
1. The fulcrum of a door is along its
hinges.
2. Pushing near the side farthest from
2.
the hinges requires the least force to
open a door.
3. The doorstop will work best near the
side farthest from the hinges.
3.
SECTION: WHAT IS ENERGY?
4.
1. The sun’s energy is captured by plants,
which are eaten as food. This food
provides a release of energy for other
uses, such as swinging the bat.
2. Yes, because the ball moves a distance
in response to the force.
3. The energy is absorbed in the glove
and hand of the fielder. Some energy is
also released as sound when the
fielder catches the ball.
SECTION: CONSERVATION OF
ENERGY
5.
effects of a force acting over a distance. W F d b. Power is a quantity that measures the rate at which
work is done. P W/t c. Mechanical
advantage (MA) is a quantity that
measures how much a machine multiplies force or distance.
MA output force/input
distance/output distance
Power is the rate at which work is
done. Power equals the amount of
work done per unit time: P W/t.
Machines make work easier by allowing you to apply less force at any given
moment.
1.8 102 J
W Fd (120 N)(1.5 m) 180 J
5.6 kW
P W/t (250 000 J)/(45 s)
5.6 103 J/s
5.6 kW
6. 4.0
MA input distance (4.8 m)
4.0
output distance (1.2 m)
SECTION: SIMPLE MACHINES
1. Answers will vary. Sample answers:
a. crowbar b. ax head c. pulley on a
flagpole d. car tire, steering wheel
e. wheelchair ramp f. machine screw,
1. The sled has the most potential energy
at the top of the hill and the least
potential energy at the bottom of the
hill.
2. The sled has the most kinetic energy
at the bottom of the hill and the least
kinetic energy at the top of the hill.
3. The potential energy decreases, the
kinetic energy increases, but the total
energy remains the same.
4. This energy is transformed into heat
by the friction between the runners of
the sled and the snow.
jar lid
2. Check students’ drawings. Labels
should show input force, output force,
and fulcrum.
3. A wedge and a screw are both modified inclined planes. A wedge functions like two inclined planes back to
back. A screw is an inclined plane
wrapped around a cylinder.
4. An inclined plane turns a small input
force into a large output force by
spreading the work out over a large
distance.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Science Spectrum
115
Work and Energy
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TEACHER RESOURCE PAGE
3. a. 60%
efficiency useful work output/work
input (45 N)/(75 N) 0.60 60%
b. 87%
efficiency (39 N)/(45 N) 0.87 87%
c. 44%
efficiency (75 N)(2.5 m)/(425 J) (187.5 J)/(425 J) 0.44 44%
4. A machine with a high efficiency will
5. A wheelbarrow is a second-class lever,
and it has a wheel-and-axle on which
it moves.
SECTION: WHAT IS ENERGY?
1. a. Kinetic energy is the energy of a
moving object due to its motion.
b. Potential energy is stored energy
resulting from the relative positions of
objects in a system. c. Mechanical
energy is the sum of the kinetic and
potential energy of large-scale objects
in a system.
2. 4.2 104 J; PE mgh (95 kg)(9.8 m/s2) (45 m) 4.2 104 J
3. 4.5 103 J; KE (1/2)mv2 (1/2)(74 kg)(11 m/s)2 4.5 103 J
4. A stretched bungee cord contains elastic potential energy.
5. In photosynthesis, energy from sunlight is captured by plants and stored
in sugars and other organic molecules.
The energy is stored in the molecules
as chemical energy, which is a form of
potential energy.
6. The kinetic energy of an object
quadruples when the speed of the
object doubles.
7. Mechanical energy is the sum of
potential and kinetic energy on a large
scale, while chemical energy is not
measured on a large scale and has little effect on large-scale systems.
Chemical energy is the energy stored
in the bonds of a chemical compound.
transfer a greater amount of the work
input to useful work output.
5. With each bounce, some of the ball’s
mechanical energy is transformed into
non-mechanical energy. With less total
mechanical energy, the ball cannot
bounce as high.
6. At the top of the hill, a skier has
mostly potential energy. As the skier
glides down the hill, that energy is
transformed into kinetic energy, and
the skier gains speed. A small amount
of the energy may be transformed into
nonmechanical energy, which may
cause the snow to melt or produce a
swooshing sound.
Science Skills
EQUATIONS WITH THREE PARTS
1. 450 N
SQUARES AND SQUARE ROOTS
1. 37 m2
3. 36.4444
2. 10.51 m
4. 12.1
PERCENTAGES
1. 62%; 44%; friend’s neighborhood
SECTION: CONSERVATION OF
ENERGY
2. 52%; 49%; ninth grade class
3. 35
1. Efficiency is a quantity that measures
the ratio of useful work output to
work input.
2. Mechanical energy can be transformed
into nonmechanical energy due to friction or air resistance, which causes an
increase in temperature in the system
or in the surrounding environment.
Mechanical energy can also be transformed into nonmechanical energy
when a sound is produced by friction
or an impact.
2. 6
Math Skills
WORK
W 2.7 J
0.60 m
F 4.5 N
W 4.35 102 J
0.600 m
d F 7.25 102 N
W 8.8 104 J
d 2.6 m
F 3.4 104 N
W 9.8 107 J
F 2.8 106 N
d
35 m
W 405 J
F 27 N
d 15 m
1. d 2.
3.
4.
5.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Science Spectrum
116
Work and Energy