Question

Section 14.3 Mechanical Advantage
and Efficiency
(pages 421–426)
This section describes mechanical advantage and efficiency and how to calculate these
values. It also discusses ways to maximize mechanical advantage and efficiency.
Reading Strategy (page 421)
Building Vocabulary As you read the section, write a definition in the table
for each vocabulary term in your own words. For more information on this
Reading Strategy, see the Reading and Study Skills in the Skills and
Reference Handbook at the end of your textbook.
Mechanical Advantage
Vocabulary Definition
Mechanical The number of times a machine increases force
advantage
Mechanical Advantage (pages 421–423)
1. The number of times that a machine increases an input force is the
of the machine.
2. Circle the letter of the correct answer. For a given input force, what
affects the output force that a nutcracker can exert on a nut?
a. the location of the hand holding the nutcracker
b. the angle of the legs of the nutcracker
c. the position of the nut
3. Mechanical advantage describes the relationship between input force
and force.
4. Is the following sentence true or false? A loading ramp with a rough
surface has a greater mechanical advantage than one with a smooth
surface.
Physical Science Reading and Study Workbook Level B ■ Chapter 14 165
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Chapter 14 Work, Power, and Machines
166 Physical Science Reading and Study Workbook Level B ■ Chapter 14
© by Savvas Learning Company LLC. publishing as Savvas Prentice Hall. All rights reserved.
5. Because friction is always present, the actual mechanical advantage
of a machine is never than its ideal mechanical
advantage (IMA).
6. A machine’s is the mechanical advantage
in the absence of friction.
Calculating Mechanical Advantage (pages 424–425)
7. Is the following sentence true or false? To calculate ideal mechanical
advantage, divide input distance by output distance, and then divide
the result by the force of friction.
8. Is the following sentence true or false? An inclined plane is an example
of a machine.
9. Calculate the IMA of a ramp for the distances given in the table.
Ideal Mechanical Advantages of Ramps
Horizontal Distance Vertical Rise IMA
1.5 meters 0.5 meters 3
12 meters 1.5 meters
3.6 meters 0.3 meters
Efficiency (pages 425–426)
10. Choose the letter of each statement that tells why the efficiency of a
machine is always less than 100 percent.
a. Machines get hot and need fans.
b. Friction must be overcome.
c. Gravity prevents machine parts from moving easily.
11. Is the following sentence true or false? To calculate the efficiency of a
machine, divide the work output by work input, and then multiply
by 100.
12. Calculate the efficiency of a machine with a work output of 120 J and
a work input of 500 J.
13. Circle the letter of the work input for a machine with a work output of
240 J and an efficiency of 80 percent.
a. 300 J b. 200 J c. 320 J
14. Reducing friction the efficiency of a machine.

Answer 1

Mechanical advantage (vocabulary): The number of times a machine increases an input force; equivalently, the ratio of output force to input force.

Mechanical Advantage (pages 421–423)
1. mechanical advantage
2. c. the position of the nut
3. input force and output force
4. False
5. greater than
6. ideal mechanical advantage (IMA)

Calculating Mechanical Advantage (pages 424–425)
7. False
8. True
9. IMA = horizontal distance / vertical rise
- 12 m / 1.5 m = 8
- 3.6 m / 0.3 m = 12

Efficiency (pages 425–426)
10. b. Friction must be overcome.
11. True
12. Efficiency = (120 J / 500 J) × 100% = 24%
13. a. 300 J
14. increases