A crane lifts a 2000 kg steel beam vertically upward at a constant speed of 2.0 m/s. What is the power output of the crane?

Core Concept

Power is the rate at which work is done. Since the beam is moving at constant velocity, the net force is zero, meaning the upward force from the crane equals the weight of the beam (mg = 2000 kg × 9.8 m/s² = 19,600 N). Power = force × velocity = 19,600 N × 2.0 m/s = 39,200 W = 39.2 kW. Option A is close to the correct answer but uses g = 10 m/s² instead of 9.8 m/s² (giving 40 kW). Option B would be correct if the velocity was 4.0 m/s. Option C would be correct if the velocity was 8.0 m/s. Option D would be correct if the velocity was 16.0 m/s.