As a result of doing work a person supplies a machine with 1100 J of energy in 12 seconds. The machine in turn does work and delivers 900 J of energy in 14 seconds to some object. what is the effiecency of this machine?

Answer 1

Efficiency = Power out/ Power in
= (900/14) / (1100/12)
= 70%

This assumes that the power is delivered continously and the stated measurements are typical of the average power in and out.

If the work were done only during a 12 second interval and then recovered or "delivered" more slowly in a following 14 sec period, the efficiency would be (work out/(work in) = 900/1100 = 81.8%