A hoist lifts a car with a total energy input of 6.73 x 104 J. The car gains 2.35 x 104 J of gravitational potential energy during the process. What is the efficiency of the hoist? A)34.9% B)25.0% C)7.00% D)17.5%
The car gains 2.35 x 10^4 J potential energy from 0 (we assume this way). Hence, the hoist must do work as much as the gained potential energy, which is 2.35 x 10^4 J. The hoist has an input energy of 6.73 x 10^4 J. The efficiency is this: 2.35 * 10^4/6.73 * 10^4 * 100% = 34.9%
