An engineer is testing the electric motor of an underwater survey drone. During a propulsion test, the motor runs steadily for 280 s. The motor produces a constant useful mechanical power output of 12.5 W and operates at an efficiency of 70%.
Calculate the total useful energy output of the motor during this test.
State the equation linking efficiency, useful energy output, and total energy input.
Calculate the total electrical energy input to the motor during this period.