An engine must do 500 joules of work to pull a 10kg load up to a height of 4meters what is the efficiency ?

Question

An engine must do 500 joules of work to pull a 10kg load up to a height of 4meters what is the efficiency ?

Answer 1

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Work = Force * Distance traveled vertically

To pick up a 10kg object for 4 meters you need to exhaust 392 joules of work (10kg * 4m * -9.8m/s^2). Since you exhausted 500 for the same effect you have wasted 108 of it presumably into heat. Hence 392/500 is your efficiency since only 392 of that 500 was used to actually lift the object.

Answer 2

PE = hmg = 4*10*9.8 = 392 J

Eff = 392/500 = 78%

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