The electric motor consumes 0.4 kWh of energy per hour and performs 1080 kJ of useful work. What is its efficiency?

The efficiency of an electric motor can be expressed by the formula:
η = A / Q, where A is the value of the perfect work by the electric motor (A = 1080 kJ = 1080 * 10 ^ 3 J), Q is the energy expended by the electric motor (Q = 0.4 kW * h = 0.4 * 3.6 * 10 ^ 6 J).
Let’s calculate the efficiency of the electric motor:
η = A / Q = (1080 * 10 ^ 3) / (0.4 * 3.6 * 10 ^ 6) = 1080000/1440000 = 0.75 = 75%.
Answer: The efficiency of the electric motor is 75%.