A machine is supplied energy at a rate of 4,000W and does useful work at a rate of 3,760W. What is the efficiency of the machine?
Let’s understand the question. You have an INPUT of 4000 W (J/s), and an OUTPUT of 3760 W (J/s). So, you have a loss of 4000W - 3760W = 240W. Since there is lost energy, the efficiency must be below 100%, which agrees with the laws of thermodynamics. On to the work:
Efficiency = 100 * [OUTPUT/INPUT] = 100 * [3760/4000] = 94% efficient.