A set of pulleys is used to raise a 200 N crate 5 m. to fo this the operator applies a force of 50 N and pulls in 25 m of rope. Find the efficiency of the pulley system.

A: 50%

B: 62.5%

C: 75%

D: 80%

- - The output work (energy) is (200 N) x (5 m) = 1,000 Joules

- - The input work (energy) is (50 N) x (25 m) = 1,250 Joules

- - Efficiency = (useful energy output) / (energy input)

Efficiency = (1,000 J) / (1,250 J)

Efficiency = 0.8 or 80% (D).