Name: ______Date: ______Period: _____

Unit 3 Section 1 Study Guide/Review

Work, Power, and Machines

  1. What is work?
  1. If you try to lift a heavy car and apply a large force but the car does not move, have you done any work? Explain why or why not.
  1. Classify the following as either work or no work.

Example / Work or No Work?
You pull books out of your book bag.
You lift a bin of newspapers.
You push on a car stuck in the snow.
You hold a heavy piece of wood in place.
You pull a sled through the snow.
You hold a bag of groceries.
  1. In order for you to do work on an object, the object must move some ______as a result of your force.
  1. What unit is work measured in?
  1. What 2 units is a Newton ∙ meter equivalent to?
  1. True or False? Lifting a heavier object demands greater force than lifting a lighter object.
  2. True or False? Moving an object a shorter distance requires more work than moving an object a greater distance.
  1. How is power defined? What is the SI unit for power? (Note: 2 other possible units for power are horsepower and joules/second.)
  1. True or False? Power is limited to situations in which objects are moved.
  1. How do machines make work easier?
  1. Do machines reduce the amount of work we have to do? If not, why are machines so useful?
  1. True or False? Because of friction, using machines increases the amount of energy that is needed to do work.
  2. True or False? Machines allow you to apply a smaller force over a larger distance.
  1. Compare Figure A with Figure B.

  1. How do the forces in each picture differ?
  1. How do the distances in each case differ?
  1. How does the total work done in each figure compare?
  1. Would you rather lift the box like in Figure A or Figure B? Why?
  1. What is mechanical advantage?
  1. What is the mechanical advantage of a ramp that is 10 meters long and 2 meters high?
  1. What does a machine with a mechanical advantage of greater than 1 do? What does a machine with a MA less than 1 do?
  1. A man pushes a crate along a factory floor by exerting a force of 50 N. If the crate moves a distance of 8.0 m, how much work does the man perform?
  1. A runner exerts a force of 510 N against the ground while running a distance of 80.0 m. The runner’s power output over this distance is 4,000 W. How much time does it take the runner to travel 80.0 m? (Note: You must first find the work.)
  1. A child pulls a little red wagon down the sidewalk and does 400.0 J of work. If the distance the wagon is pulled is 50.0 m, what is the force exerted?
  1. You must exert a force of 5.0 N on a book to slide it across a table. If you do 3.0 J of work in the process, how far have you moved the book?
  1. My husband, Nick, lifts a weight and applies a force of 700.0 N to move it 0.50 m above his head in 1.71 seconds. What is his power output? (Note: You must first find work.)
  1. A ship’s diesel engine has a power output of 3,100,000 W. How much work is done by the engine in 2100 s?
  1. A car breaks down 2.1 m from the shoulder of the road. 1990 N of force is used to push the car off the road. How much work has been done on the car?
  1. Power is calculated by dividing work by ______.
  1. ______is a quantity that measures the effects of force acting over a distance.
  1. ______is a quantity that measures the rate at which work is done.