A 24-volt motor of 1/5 horsepower operating at 75 percent efficiency requires approximately how many watts of electrical input power?

• A. 150 W
• B. 199 W
• C. 100 W
• D. 300 W

Answer: (B)

The main idea is that input electrical power equals the mechanical output power divided by the efficiency: P_in = P_out / η. The motor’s output is 1/5 horsepower, which is 0.2 hp. Convert to watts: 0.2 × 746 ≈ 149 W of mechanical output. With 75% efficiency (0.75), the electrical input needed is 149 W / 0.75 ≈ 199 W. So the required input power is about 199 watts. The 24 V rating isn’t needed for this calculation, but it would imply a current around 199 W / 24 V ≈ 8.3 A.