Work and Machines

What is the definition of work?

• A job that completes a task

• Energy transferred when a force makes an object move

• Earning money

• Using a computer

If you push against an object and it doesn't move, are you doing work?

• No

• Yes

In order for work to be done, what two things need to happen?

• Object needs to move in any direction

• Object needs to have acceleration and speed

• Object must move and must move in the direction of the force applied

• Object needs to feel force, it doesn't matter if it moves

A ___________ is a device that changes the force or increases the motion from work.

• Work

• Job

• Machine

• Calculator

What is the equation for efficiency (%)

• output work divided by input work x 100

• input work divided by output work x 100

• output work divided by net force x 100

• Input work divided by net force x 100

Machines can be made more efficient by ____________.

• Increasing input

• Decreasing energy

• Increasing friction

• Reducing friction

What is the SI unit for work?

• Newtons

• Joules

• Grams

What is the mechanical advantage for a crate that weighs 950 N and is lifted with a pulley force of 250 N.

• 1.5

• 2.0

• 3.8

• 4.0

You do 20 J of work in pushing a crate up a ramp. If the output work from the inclined plane is 11 J, then what is the efficiency of the inclined plane?

• 55%

• 45%

• 55J

• 55N

What is the equation for calculating work? 

• force times distance 
• force divided by distance 
• force plus distance 
• mass times acceleration