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Work and Power Practice Problems. Can you answer these 4 work and power practice...

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matthew0109 | Student | Honors

Posted November 14, 2011 at 5:33 AM via web

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Work and Power Practice Problems.

Can you answer these 4 work and power practice problems. I am having some trouble.

1. A mover is loading a 253kg crate of hammers onto a truck. The upward force on the crate is 2470 N (newtons), and 3650 J(joules) of work are required to raise the crate from the pavement to the truck bed.

a. How far is the crate lifted?

b. If the mover does this in 4s, how powerful is he?

 

2. In the human cannonball a person is shot from a cannon with a barrel that is 3.05cm long. 1600 J (joules) of work are done to accelerate the acrobat out of the cannon. What is the force exerted on the acrobat?

3. A runner exerts a force of 334 N (newtons) against the ground while running a distance of 50.0m. The runner's power over this distance is 3.71kW (kilowats). How much time does it take the runner to travel 50.0m? (convert kW to W)

4. A car has run out of gas. Fortunately, there is a gas station nearby. You must exert a force of 715 N (newtons) on the car in order to move it. By the time you reach the station, you have done 27200 J (joules) of work. How far have you moved the car?

 

1 Answer | Add Yours

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ndnordic | High School Teacher | (Level 2) Associate Educator

Posted November 14, 2011 at 8:42 AM (Answer #1)

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There are two basic equations you need to use:  W = Fd where W is the work done in joules, F is the force in Newtons, and d is the distance in meters.

The other is Power = W/t, where power is measured in watts (W), work in joules (J), and time in seconds (s)

1a.   W = 3650 J, F = 2470 N, find d

d = W/F = 3650/2470 = 1.478 m

1b. P = W/t          W = 3650 J,  t = 4 s

P = 3650/4 = 912.5 W (1 hp = 746 W) so this is equal to 1.22 HP)

2.  I think the length is probably 3.05 m, not cm.

W = Fd   w = 1600J, d = 3.05 m, find F

F = W/d = 1600/3.05 = 524.6 N

3.  this is a two part problem. First find W, then find time.

W = Fd = 334 N * 50 m = 16700 J

P = W/t

P = 3.71 kW = 3710 W

3710 = 16700/t

t = 16700/3710 = 4.5 s

4.  W = Fd

W = 27200 J, F = 715N, find d

d = W/f = 27200/715 =38.04 m

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