16 August, 21:47

# After a large snowstorm you shovel 2000 kilograms of snow off your side walk in 1 hour. you lift the shovel to an average height of 1.25 meters while you are piling the snow in your yard. how much work did you do?

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1. 16 August, 22:10
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Lifting a mass to a height, you give it gravitational potential energy of

(mass) x (gravity) x (height) joules.

To give it that much energy, that's how much work you do on it.

If 2,000 kg gets lifted to 1.25 meters off the ground, its potential energy is

(2,000) x (9.8) x (1.25) = 24,500 joules.

If you do it in 1 hour (3,600 seconds), then the average power is

(24,500 joules) / (3,600 seconds) = 6.8 watts.

None of these figures depends on whether the load gets lifted all at once,

or one shovel at a time, or one flake at a time.

But this certainly is NOT all the work you do. When you get a shovelful

of snow 1.25 meters off the ground, you don't drop it and walk away, and

it doesn't just float there. You typically toss it, away from where it was laying

and over onto a pile in a place where you don't care if there's a pile of snow

there. In order to toss it, you give it some kinetic energy, so that it'll continue

to sail over to the pile when it leaves the shovel. All of that kinetic energy

must also come from work that you do ... nobody else is going to take it

from you and toss it onto the pile.