Physical Science
Simple Machines Review
Name_____________________
Period ____________________
Conceptual Questions
1. What is a simple machine?
A simple machine is a device that makes doing work easier.
2. Can a simple machine do work for you?
No, a machine only makes doing work easier. You still have to input work to make the
machine do anything.
3. What is Actual Mechanical Advantage?
This is the number of times that a machine increases your input force.
4. What is Ideal Mechanical Advantage?
This is the number of times that a machine increases your input force, if there is no friction in
the system.
5. What is efficiency?
Efficiency is the percentage of work output compared to work input. It can never be greater
than 100% and for all realistic machines the efficiency will be less than 100%.
6. What is a lever?
A lever is a rigid beam that rotates around a fulcrum point.
7. Describe a 1st class lever.
The fulcrum of a first class lever is in between the input force and the output force.
8. What are some examples of a 1st class lever?
A balance, See-Saw and crowbar.
9. Describe a 2nd Class lever.
The fulcrum for a 2nd class lever is at one end, the output force is in the middle and the input
force is at the opposite end.
10. What is an example of 2nd class lever?
A wheelbarrow.
11. What is a 3rd Class Lever?
The fulcrum of a third class lever is at one end, the input force is in the middle and the output
force is at the opposite end.
12. What are some examples of 3rd class levers?
The human arm, baseball bat and hockey stick.
13. How do you find the IMA of a lever?
You divide the input arm by the output arm.
14. How do you find the MA of a lever?
You divide the output force by the input force.
15. What is a ramp?
A ramp is an inclined plane that is used to lift an object more easily.
16. What are some examples?
Wheelchair ramps, moving ramps on trucks, a winding road that snakes up a hillside.
17. How do you find the IMA of a ramp?
To find the IMA you divide the ramp length by the ramp height.
18. What is a pulley?
A pulley is a grooved wheel that a rope fits into.
19. How do you find the IMA of a pulley system?
Count the number of rope sections that help to support the weight.
20. How do you find the AMA of a pulley system?
Divide the force output by the force input.
Practice Problems:
1. If you do 25 J of work on a lever, and the lever does 20 J of work on a mass for you, what is its
efficiency?
𝑬𝒇𝒇𝒊𝒄𝒊𝒆𝒏𝒄𝒚 =
𝑾𝒌 𝑶𝒖𝒕
𝑾𝒌 𝑰𝒏
× 𝟏𝟎𝟎%
𝑬𝒇𝒇𝒊𝒄𝒊𝒆𝒏𝒄𝒚 =
𝟐𝟎𝑱
×
𝟐𝟓𝑱
𝟏𝟎𝟎%
𝑬𝒇𝒇𝒊𝒄𝒊𝒆𝒏𝒄𝒚 = 𝟖𝟎%
2. During a lab, your partner moves the input arm of a lever down 5cm. You notice the output arm
moving 10cm upwards. What is the IMA of this lever?
𝑰𝑴𝑨 =
𝑰𝒏𝒑𝒖𝒕 𝑨𝒓𝒎
𝑶𝒖𝒕𝒑𝒖𝒕 𝑨𝒓𝒎
𝑰𝑴𝑨 =
𝟓𝒄𝒎
𝟏𝟎𝒄𝒎
𝑰𝑴𝑨 = 𝟎. 𝟓
3. While working with a pulley system, you find it takes 2.45 N to move a 9.8 N mass.
a. What is the pulley system’s MA?
𝑴𝑨 =
𝑶𝒖𝒕𝒑𝒖𝒕 𝑭𝒐𝒓𝒄𝒆
𝑰𝒏𝒑𝒖𝒕 𝑭𝒐𝒓𝒄𝒆
𝑴𝑨 =
𝟗.𝟖𝑵
𝟐.𝟒𝟓𝑵
𝑴𝑨 = 𝟒
b. If the mass rises a distance of 2m while you pull on the string in the above question,
how much work did the pulley system do?
𝑾𝒌 𝒐𝒖𝒕 = 𝑭𝒐𝒖𝒕 × 𝒅𝒐𝒖𝒕
𝑾𝒌 𝒐𝒖𝒕 = 𝟗. 𝟖𝑵 × 𝟐𝒎
𝑾𝒌 𝒐𝒖𝒕 = 𝟏𝟗. 𝟔𝑱
c. If you pulled the string a distance of 9m, how much work did you do on the pulley
system?
𝑾𝒌 𝒊𝒏 = 𝑭𝒊𝒏 × 𝒅𝒊𝒏
𝑾𝒌 𝒊𝒏 = 𝟐. 𝟒𝟓𝑵 × 𝟗𝒎
𝑾𝒌 𝒊𝒏 = 𝟐𝟐. 𝟎𝟓𝑱
d. What is the efficiency of the pulley system?
𝑬𝒇𝒇𝒊𝒄𝒊𝒆𝒏𝒄𝒚 =
𝑾𝒌 𝑶𝒖𝒕
𝑾𝒌 𝑰𝒏
× 𝟏𝟎𝟎%
𝑬𝒇𝒇𝒊𝒄𝒊𝒆𝒏𝒄𝒚 =
𝟏𝟗.𝟔𝑱
×
𝟐𝟐.𝟎𝟓𝑱
𝟏𝟎𝟎%
𝑬𝒇𝒇𝒊𝒄𝒊𝒆𝒏𝒄𝒚 = 𝟖𝟖. 𝟗%
4. A moving truck is equipped with a ramp that can be pulled out from its bed, which is 1.25
meters above the ground. When fully extended the ramp is 5 meters long. Using this ramp a
person can move a refrigerator weighing 3000 N by exerting only 800 N of force. What is the
work input, work output, AMA, IMA and efficiency of this ramp?
Work Input = 4000J
Work Output = 3750J
AMA = 3.75
IMA = 4
Efficiency = 93.75%
5. This problem was corrected. The height should be 10m. A pulley system is used to lift a stack of
cinder blocks weighing 10,000 N to a height of 10 meters. A crane provides a total force of 1200 N
at one end of a cable, which must be pulled a distance of 90 m. What is the work input, work
output, AMA, IMA and efficiency of this pulley system?
Work Input = 108,000J
Efficiency = 92.6%
Work Output = 100,000J
AMA = 8.33
IMA = 9