Question

250 N force is required to raise 75 kg mass from a pulley. If rope is pulled 12 m then the load is lifted to 3m, the efficiency of pulley system will be : -

• A. 0.25
• B. 0.333
• C. 0.75
• D. 0.9

Answer 1

Answer: (C)

0.75

Answer 2

Efficiency of the system is $\eta = \frac{output \; work}{input \; work}$
Input work = Fs = $250 \times 12$
Output work = mgh = $75 \times 10 \times 3$
So, $\eta = \frac{ 75 \times 10 \times 3}{250 \times 12} = 0.75 = 75$