John lifts a 3.0kg suitcase a distance of 1.2m such that it's above his head. If he has an efficiency of 35%

Question

find how much work he had to do in order to lift it.

The answer is 1.0*10^2J, but I can't seem to calculate this. Can someone please explain to me?

Answer 1

he'll need to exert a force of 3*g newtons to lift it and he needs to apply it through 1.2 m so doing 3*g*1.2 J work. at 35% efficiency that means 3*g*1.2/0.35 energy expended.