How much work is done on a 100-kg crate that is hoisted 3 m in a time of 2 s?

Answer 1

-- The force required to lift the crate is equal to its weight.

-- Weight of the crate = (M x g) = 100 x 9.8 = 980 newtons.

-- Work = (force x distance) = 980 x 3 = 2,940 newton-meters = 2,940 joules.

That's the work done to lift the crate, whether the worker takes a millisecond or

a month to do the job. The amount of work the job requires doesn't depend on

how fast it's done.

The rate at which the work is done is called power.

-- If the work is done in 2 seconds, the power is 2,940/2 = 1,470 joules/second = 1,470 watts.

-- If you're being paid by the hour, decide to stretch it out, and take exactly one hour

to do it, then the power is 2,940/3,600 = 0.817 watt.

-- If you're trying to make a good impression on the boss, and you complete the hoist in

1 millisecond, then your power level is 2,940/0.001 = 2,940 kilowatts = 2.94 megawatts.

-- If you could have completed the job a tiny bit faster ... in 1.97 rather than 2.0 seconds ...

then the power would have been 2,940/1.97 = 1,492 watts = exactly 2 horsepower.

But the amount of work is the same in every case.