Introduction to Machines

The ratio of output force to input force is the __________ of a machine.

NOT "mechanical advatage"

Which statement best describes why a machine is useful?

NOT A machine can decrease both the input force and the input distance needed to do a given amount of work.

A machine has an efficiency of 80%. How much work must be done on the machine so to make it do 50,000 J of output work?

62,500 J

Lucy needs to lift a crate to a shelf 20 m high. She does 12,000 J of work on a machine to help her. The machine exerts a force of 500 N to lift the crate.

NOT 24%

Lucy needs to lift a crate to a shelf 20 m high. She does 12,000 J of work on a machine to help her. The machine exerts a force of 500 N to lift the crate. What is the efficiency of the machine?

NOT 4.2%

The ratio of output work to input work expressed as a percent is the _______ of a machine.

"efficiency"

A machine can never be 100% efficient because some work is always lost due to _______ .

"friction"

A machine has an efficiency of 70%. How much work does the machine do when 20,000 J of work is done on it?

14,000 J

What is the mechanical advantage of a machine that applies a force of 1000 N to an object when a force of 500 N is applied to the machine?

2

How does using a ramp make work easier when loading a piano onto a truck three feet above the ground?

It allows a smaller force to be applied over a longer distance.

A machine has a mechanical advantage of 4.5. What force is put out by the machine if the force applied to the machine is 800 N?

3600 N

Mr. Franklin uses a machine that has an efficiency of 80%. The machine applies a force of 800 N through a distance of 20 m. Mr. Franklin applies a force of 50 N on the machine. Through what distance does Mr. Franklin apply the force?

400 m

A machine has a mechanical advantage of 5. What force should be applied to the machine to make it apply 3000 N to an object?

600 N

Which statements describe how a machine can help make work easier? Check all that apply.

NOT It can increase the amount of work performed if the output force is in the same direction as the input force. It can apply a force to an object in a different direction than the force applied to the machine. It can increase the distance through which a force acts by exerting less force than was used on it.

Which is a result of using a machine?

NOT The mechanical advantage makes the work output greater than the work input.

What is impossible for a machine to do?

NOT apply a force that is less than the force that is applied to the machine