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Name: ________________________ Class: ___________________ Date: __________
ID: A
Chapter 08 Multi-format Test
Modified True/False
Indicate whether the statement is true or false. If false, change the identified word or phrase to make the statement true.
____
1. The rate of doing work is called energy. _________________________
____
2. Work is the form of energy that comes from applying a force over distance. _________________________
____
3. The amount of work done on an object always equals the amount of energy transferred to that object.
_________________________
____
4. 746 watts is equal to 1 kilowatt. ____________________
____
5. The unit for power equal to one joule of work divided by one second of time is called a watt.
_________________________
____
6. The work a machine does for you is called the input work. _________________________
____
7. The measure of how effective a machine is in using its energy to do work is known as the
friction of the machine. _________________________
Completion
Complete each statement.
Select the correct term to complete each sentence. There are extra terms in the list.
work
newtons
greater than
work output
power
energy
less than
joules
efficiency
force
work input
horsepower
8. When a force is applied that moves an object in the direction of the applied force, ____________________ is
done.
9. Both work and energy are measured in the SI unit of ____________________.
10. For an object to do work, it must possess ____________________.
11. The ratio of the work output to the work input is called the ____________________.
12. The rate at which work is done is called ____________________.
13. Work output can never be __________________ work input.
14. The work that is done on an object is called the ____________________.
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ID: A
Matching
Match each unit to a quantity that it measures.
a. efficiency
b. work
c. power
d. force
____
____
____
____
____
15.
16.
17.
18.
19.
joule
newton
watt
percent
horsepower
Short Answer
20. Calculate the work done when a 50-newton object is lifted 5 meters using a block and tackle.
21. Compare the size of the power units: watt, kilowatt and horsepower.
22. On Monday, Bik runs upstairs carrying a heavy book. The next day, she walks upstairs carrying the same
book. Compare Bik’s work and power on Monday and Tuesday.
23. Compare the output work to the input work for a machine.
Problem
24. A 2.0 kilogram mass is pushed along a horizontal surface by a 3.0 newton force. How much work is done in
moving the object 1.5 meters?
25. Calculate the work required to move a 2,000-kilogram automobile to the top of a 100-meter hill.
26. What is the efficiency of a machine that requires work input of 15 joules to lift a 4-newton object 3 meters?
27. How long will it take a machine to do 5000 joules of work if the power rating of the machine is 100 watts?
Essay
28. Isaiah and Ben have a race to carry identical objects from a point at the bottom of a hill to the same point at
the top. Isaiah runs straight up a very steep part of the hill and finishes first. Ben chooses a more gradual
ascent and, walking, arrives after Isaiah. Who has done more work? Explain your answer.
29. Describe how the efficiency of a machine may be increased. Name at least three examples.
30. Explain why the efficiency of machines is always less than 100 percent. In the discussion, use the words
efficiency, work input, work output, heat, and friction.
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ID: A
Chapter 08 Multi-format Test
Answer Section
MODIFIED TRUE/FALSE
1. ANS: F, power
DIF: basic
REF: section 8.1
2. ANS: T
3. ANS: T
4. ANS: F, horsepower
DIF: basic
DIF: basic
REF: section 8.1
REF: section 8.1
DIF: basic
5. ANS: T
6. ANS: F, output
DIF: basic
REF: section 8.2
REF: section 8.2
DIF: basic
REF: section 8.2
7. ANS: F, efficiency
DIF:
basic
REF: section 8.2
COMPLETION
8. ANS: work
DIF: basic
9. ANS: joules
REF: section 8.1
DIF: basic
10. ANS: energy
REF: section 8.1
DIF: basic
11. ANS: efficiency
REF: section 8.1
DIF: basic
12. ANS: power
REF: section 8.2
DIF: basic
13. ANS: greater than
REF: section 8.2
DIF: basic
14. ANS: work input
REF: section 8.2
DIF:
basic
REF: section 8.2
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ID: A
MATCHING
15.
16.
17.
18.
19.
ANS:
ANS:
ANS:
ANS:
ANS:
A
D
C
B
C
DIF:
DIF:
DIF:
DIF:
DIF:
basic
basic
basic
basic
basic
REF:
REF:
REF:
REF:
REF:
section 8.1
section 8.1
section 8.2
section 8.2
section 8.2
SHORT ANSWER
20. ANS:
work = force × distance
work = 50 newtons × 5 meters
work = 250 joules
DIF: intermediate REF: section 8.1
21. ANS:
The watt is the smallest of the three, and is equal to 1 joule/second. Next largest is one horsepower, which is
equal to 746 watts. The largest is the kilowatt, which is 1000 times larger than 1 watt.
DIF: intermediate REF: section 8.2
22. ANS:
The work done by Bik on both days is the same, but she generated more power on Monday because she did
the same amount of work in less time.
DIF: intermediate REF: section 8.2
23. ANS:
The work output is never greater than the work input. The work output could only equal the work input in a
perfect machine.
DIF:
intermediate
REF: section 8.2
PROBLEM
24. ANS:
work = force × distance
work = 3 N × 1.5 m
work = 4.5 J
DIF: intermediate REF: section 8.1
25. ANS:
work = 130,667 watts
work = force × distance = mass × g × height
work = 2,000 kg × 9.8 m/s2 × 100 m
work = 1,960,000 joules
DIF:
intermediate
REF: section 8.1
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26. ANS:
Efficiency =
work out
4N×3m
× 100 =
work in
15 J
Efficiency =
4N×3m
× 100
15 J
Efficiency = 80%
DIF: intermediate REF: section 8.2
27. ANS:
power = work ÷ time
time = work ÷ power
time = 5,000 J ÷ 100 W
time = 50 s
DIF:
advanced
REF: section 8.2
ESSAY
28. ANS:
Isaiah and Ben do the same amount of work. The work is done against gravity:
work = mass × g × height.
Since the objects are identical, they have the same mass and are lifted the same distance against gravity. The
value for g, the acceleration due to gravity, is a constant for the objects. The work done is independent of the
path. (Because Isaiah finished the work in less time, he did produce more power.)
DIF: intermediate REF: section 8.1
29. ANS:
Answers will vary. Sample answers include:
An important way to increase the efficiency of a machine is to reduce friction. This may be done by using ball
bearings and oil. Slippery substances, such as Teflon™, reduce sliding friction. Streamlined shapes will
reduce air friction in properly designed cars.
DIF: basic
REF: section 8.2
30. ANS:
In a machine, surfaces rubbing together causes friction. The friction produces heat, which increases the
temperature of the surrounding air and the machine. The heat dissipated to the air and the machine reduces the
work output to a level less than the work input. Since the efficiency of a machine is the ratio of the work
output to the work input, the efficiency of all machines is less than 100%.
DIF:
intermediate
REF: section 8.2
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Chapter 08 Multi-format Test [Answer Strip]
F
_____
1.
T
_____
2.
T
_____
3.
F
_____
4.
T
_____
5.
F
_____
6.
F
_____
7.
A
_____
D
_____
C
_____
B
_____
C
_____
15.
16.
17.
18.
19.
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ID: A