True/False
Indicate whether the sentence or statement is true
or false.
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1.
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Holding a 25-N bag of sugar 1 meter above the floor requires 25 joules of
work.
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2.
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The
work done by a machine is called the output work.
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3.
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The
mechanical advantage of a machine that only changes the direction of a force is one.
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4.
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Efficiency compares the output work to the output force.
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5.
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A
wheel and axle is a compound machine.
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6.
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A
second-class lever always multiplies distance.
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7.
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The
ideal mechanical advantage of a wheel and axle is the radius of the wheel times the radius of the
axle.
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8.
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Your
jaw and teeth act together as a simple machine.
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9.
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When
you raise your leg, the knee acts as a fulcrum for the upper leg.
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10.
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You
do work on an object when you lift it from the floor to a shelf.
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Multiple Choice
Identify the
letter of the choice that best completes the statement or answers the question.
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11.
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For
work to be done on an object, such as pushing a child on a swing, a. | some force need
only be exerted on the object. | b. | the object must move some distance as a result of a
force. | c. | the object must move, whether or not a force is exerted on
it. | d. | the object must
move a distance equal to the amount of force exerted on it. | | |
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12.
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Which
of these is an example of work being done on an object? a. | holding a heavy
piece of wood at a construction site | b. | trying to push a car that doesn’t move out of deep
snow | c. | pushing a child
on a swing | d. | holding a door shut on a windy day so it doesn’t blow
open | | |
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13.
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If
you exert a force of 20 newtons to push a desk 10 meters, how much work do you do on the
desk? a. | 200
joules | b. | 30 joules | c. | 10
joules | d. | 100 joules | | |
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14.
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Work
is measured in a. | meters. | b. | pounds. | c. | joules. | d. | newtons. | | |
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15.
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What
do machines do? a. | change force or
distance | b. | increase work | c. | decrease
work | d. | eliminate
friction | | |
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16.
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Pulling down on a rope to hoist a sail on a sailboat is an example of a
machine a. | multiplying
force. | b. | multiplying distance. | c. | changing
direction. | d. | reducing friction. | | |
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17.
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If
you exert a force of 20 newtons on a can opener, and the opener exerts a force of 60 newtons on the
can, the ideal mechanical advantage of the can opener is
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18.
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Without friction there would be a. | less machine efficiency. | b. | greater output
work than input work. | c. | greater input work than output work. | d. | equal input and
output work. | | |
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19.
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An
ideal machine would have an efficiency of a. | 1 percent. | b. | 10
percent. | c. | 50 percent. | d. | 100
percent. | | |
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20.
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The
efficiency of a machine compares a. | force to mass. | b. | output work to
input work. | c. | force to friction. | d. | friction to
mass. | | |
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21.
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A
ramp is an example of a simple machine called a(n) a. | inclined
plane. | b. | wedge. | c. | lever. | d. | pulley. | | |
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22.
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The
ideal mechanical advantage for an inclined plane is equal to the length of the incline divided by
the a. | mass of the
incline. | b. | slope of the incline. | c. | height of the
incline. | d. | angle of the incline. | | |
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23.
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Which
of these is an example of a third-class lever? a. | scissors | b. | pliers | c. | fishing pole | d. | nutcracker | | |
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24.
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The
ideal mechanical advantage of a wheel and axle is equal to the a. | radius of the
wheel divided by the radius of the axle. | b. | radius of the axle divided by the radius of the
wheel. | c. | radius of the wheel divided by the length of the
axle. | d. | length of the axle divided by the radius of the
wheel. | | |
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25.
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A
machine that utilizes two or more simple machines is called a a. | combination
machine. | b. | compound machine. | c. | mechanical
machine. | d. | mixed machine. | | |
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26.
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One
example of a compound machine is a a. | door. | b. | pair of
scissors. | c. | bicycle. | d. | shovel. | | |
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27.
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Which
body parts act as the fulcrums of levers? a. | muscles | b. | bones | c. | joints | d. | tendons | | |
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28.
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Which
body parts are shaped like wedges? a. | muscles | b. | tendons | c. | incisors | d. | bones in your
legs | | |
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29.
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A
simple machine that might be thought of as an inclined plane that moves is a a. | lever. | b. | wheel and axle. | c. | wedge. | d. | pulley. | | |
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30.
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Which
of these could be considered an inclined plane wrapped around a cylinder? a. | lever | b. | screw | c. | wheel and
axle | d. | pulley | | |
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31.
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The
fixed point that a lever pivots around is called the a. | axle. | b. | pulley. | c. | gear. | d. | fulcrum. | | |
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32.
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In
order to do work on an object, the force you exert must be a. | the maximum
amount of force you are able to exert. | b. | in the same direction as the object’s
motion. | c. | in a direction opposite to Earth’s gravitational
force. | d. | quick and deliberate. | | |
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33.
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Work
= force • a. | energy. | b. | velocity. | c. | distance. | d. | mass. | | |
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34.
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When
you raise or lower a flag on a flagpole, you are using a a. | wheel and
axle. | b. | pulley. | c. | wedge. | d. | inclined plane. | | |
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35.
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A
term that means the same thing as output force is a. | input force. | b. | resistance
force. | c. | effort force. | d. | multiplying
force. | | |
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36.
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A
device with toothed wheels that fit into one another is called a a. | system of
gears. | b. | wheel and axle. | c. | pulley. | d. | fulcrum. | | |
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37.
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How
can a hockey stick be considered a machine? a. | It multiplies force. | b. | It multiplies
distance. | c. | It changes direction. | d. | It reduces
friction. | | |
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38.
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The
mechanical advantage of a machine that changes the direction of force only is a. | 1 | b. | less than 1. | c. | greater than
1. | d. | zero. | | |
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39.
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Most
machines in your body, which consist of bones and muscles, are a. | wedges | b. | levers. | c. | pulleys. | d. | compound machines. | | |
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40.
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If
tight scissors have an efficiency of 50 percent, how much of your work is wasted overcoming
friction? a. | all of
it | b. | none of
it | c. | one
half | d. | 10
percent | | |
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Completion
Complete each sentence or statement.Use each of the
words once
Earth
horizontal
joule 1
input
distance
actual
friction
100 70%
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41.
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When
you drop a rock, the object that does work on the rock as it falls is
____________________.
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42.
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A
gardener pushes on the angled handle of a lawnmower, causing it to move forward across a lawn. The
only portion of the gardener’s force that does work on the lawnmower is the force in the
____________________ direction.
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43.
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A
newton-meter is a measure of work also known as the ____________________.
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44.
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The
amount of work done in lifting a 25-N bag of sugar 2 meters is the same as lifting two 25-N bags of
sugar ____________________ meter(s).
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45.
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The
force applied to a machine is called the ____________________ force.
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46.
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A
simple machine makes work easier by multiplying force or ____________________, or by changing
direction.
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47.
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The
____________________ mechanical advantage of a machine cannot be predicted in advance because it
depends on the efficiency of the machine.
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48.
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The
ideal mechanical advantage would equal the actual mechanical advantage if there were no losses due to
____________________.
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49.
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The
efficiency of an actual machine is always less than ____________________%.
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50.
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The
output work of a certain machine is 12,600 J. If the input work is 18,000 J, the efficiency is
____________________.
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