Name ______date ______period _____

Work, Power, & Machines

Work

  1. A book weighing 1.0 N is lifted 2 meters. How much work was done?
  2. A force of 15 N is used to push a box along the floor a distance of 3m. How much work was done?
  3. A student lifts a box of books that weighs 185N. The box is lifted 0.800m. How much work does the student do on the box?
  4. Two students together exert a force of 825 N in pushing a car 35m.
  5. How much work do they do on the car?
  6. If the force were doubled, how much work would they do pushing the car the same distance?
  7. A 0.189 kg ball falls 2.5m. How much work does the force of gravity do on the ball?
  8. It took 50 joules to push a chair 5 meters across the floor. With what force was the chair pushed?
  9. A force of 100 newtons was necessary to lift a rock. A total of 150 joules of work was done. How far was the rock lifted?
  10. A forklift raises a box 1.2 m doing 7.0kJ of work on it. What is the mass of the box?
  11. It took 500 newtons of force to push a car 4 meters. How much work was done?
  12. A young man exerted a force of 9,000 N on a stalled car but was unable to move it. How much work was done?
  13. You and a friend each carry identical boxes to a room one floor above you and down the hall. You choose to carry it first up the stairs, then down the hall, Your friend carries it down the hall then up another stairwell. Who does more work? Explain

Power

  1. A set of pulleys is used to lift a piano weighing 1,000 N. The piano is lifted 3 meters in 60 seconds. How much power is used?
  2. How much power is used if a force of 35 N is used to push a box a distance of 10 m in 5 s?
  3. What is the power of a kitchen blender if it can perform 3,750 joules of work in 15 seconds?
  4. How much work is done using a 500 watt microwave oven for 5 minutes?
  5. How much work is done using a 60-watt light bulb for 1 hour?
  6. Oliver weighs 600. N. He climbs a flight of stairs that is 3.0 meters tall in 4.0 seconds.

a. How much work did he do?

b. What was Oliver’s power in watts?

18. An elevator weighing 6,000 N moves up a distance of 10.0 meters in 30.0 seconds.

a. How much work did the elevator’s motor do?

b. What was the power of the elevator’s motor in watt and in horsepower?

19. After a large snowstorm, you shovel 2,500 kilograms of snow off of your sidewalk in half an hour. You liftthe shovel to an average height of 1.5 meters while you are piling the snow in your yard.

a. How much work did you do? Hint: The force is the weight of the snow.

b. What was your power in watts? Hint: You must always convert time to seconds when calculating power.

20. A television converts 12,000 joules of electrical energy into light and sound every minute. What is the powerof the television?

21. The power of a typical adult’s body over the course of a day is 100 watts. This means that 100 joules ofenergy from food are needed each second.

a. An average apple contains 500,000 joules of energy. For how many seconds would an apple power aperson?

b. How many joules are needed each day?

c. How many apples would a person need to eat to get enough energy for one day?

22. A mass of 1,000 kilograms of water drops 10.0 meters down a waterfall every second.

a. How much potential energy is converted into kinetic energy every second?

b. What is the power of the waterfall in watts and in horsepower

23. An alkaline AA battery stores approximately 12,000 J of energy. A small flashlight uses two AA batteriesand will produce light for 2 hours. What is the power of the flashlight bulb? Assume all of the energy in the batteries is used..

Mechanical Advantage

Sample problem

A wheelbarrow has a mechanical advantage of 2.2. The output distance extends from the load’s center of mass to the wheel and the input distance is from the handles to the wheel. For an output distance of 0.45 m, what is the input distance?

1. List the given and unknown values.

Given: mechanical advantage = 2.2

output distance = 4.5 m

Unknown: input distance = ? m

2. Use the mechanical advantage equation, and rearrange it to solve for output distance and input distance.

mechanical advantage = output force / input force

input force= output force / mechanical advantage

output force= mechanical advantage x input force

3. Substitute output distance and mechanical advantage values into the equation, and solve.

input distance = mechanical advantage x output distance

input distance = 2.2 x 4.5 m

input distance = 0 .99 m

  1. If an input force of 202 N is applied to the handles of the wheelbarrow in the sample problem, how large is theoutput force that just lifts the load? (Hint: Look at the mechanical advantage for the above sample problem!)
  2. Suppose you need to remove a nail from a board by using a claw hammer. What is the input distance for aclaw hammer if the output distance is 2.0 cm and the mechanical advantage is 5.5?
  3. A mover uses a ramp to load a crate of nails onto a truck. The crate, which must be lifted an output distance of1.4 m from the street to the bed of the truck, is pushed along the length of the ramp. If the input distance on theramp is 4.6 m long and friction between the ramp and crate can be ignored, what is the mechanical advantage ofthe ramp?
  4. it has been proposed that the stones of the Pyramids in Egypt were raised by using ramps. Suppose one of theseramps had a mechanical advantage of 3.86. If an input force of 6350 N was provided by laborers, what would theoutput force on the stone have been?
  5. To pry a nail out of a wall, you can apply a force of 50 N to the hammer. The hammer applies a force of 650 N to the nail. What is the mechanical advantage of the hammer?
  6. To lift a block on a movable pulley, you can apply a force of 50 N to a rope. The rope applies a force of 700 N to the block. What is the mechanical advantage of the rope?

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