the efficiency of a machine is 80% determine the work done of a person using the machine to raise a load of 250kg through a vertical distance of 3.0m (take g =10ms-2).

Answer 1

g is not 10m/s^2 anywhere on Earth. I have never understood folks doing that, unless they do not know how to use a calulator.

work= 250*g*3.0 /.80

Answer 2

F = M*g = 250*10 = 2500 N.
Wo = F*d = 2500*2500*3 = 7500 J.

Wo/Wi = 0.8,
7500/Wi = 0.8,
Wi =