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Section 2 - Using Machines Review
1. Why do we use machines?
2. What are three ways that machines make work easier?
3. In the example of a screwdriver being used by a person, who/what is doing the work input and
who/what is doing the work output?
4. What is ideal mechanical advantage?
5. Would you rather have a machine that has 20% efficiency, or a machine that has 80% efficiency if
you were the owner of a factory? Why?
6. How much force would be needed to push a box weighing 30 N up a ramp that has an ideal
mechanical advantage of 3? Assume there is no friction.
7. A carpenter uses a crowbar to remove the top of a box. The top has a resistance of 500 N. The
carpenter applies an effort force of 250 N. What is the mechanical advantage of the crowbar?
8. Calculate the efficiency of a machine that requires 20 J of input work to do 10 J of output work.
9. Calculate the mechanical advantage of a machine that changes an input force of 50 N into an output
force of 150 N.
10. Explain why a real machine’s efficiency is always less than 100%.
11. Calculate the mechanical advantage of a hammer if the input force is 125 N and the output force is
2000 N.
12. Find the efficiency of a machine that does 800 J of work if the input work is 2400 J.
13. Find the force needed to lift a 2000 N weight using a machine with a mechanical advantage of 15.