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

September 23, 2021 | education

| 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%.

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