Imagine that you plan to generate electrical power for your 60W study lamp by raising an object of mass 32kg a vertical distance of 2.5m with a rope, wrapping the rope around the axle of an electrical generator, and then allowing the object to sink slowly back to the floor (unwrapping the rope and thus turning the generator).
About how long will it take the mass to sink to the floor if the generator is to produce electrical power at a roughly constant rate of 60W? (Assume 100% efficiency.)
I know the answer is 13 seconds but how do you get to the answer? I can't even picture this T_T.