2001 AIPMT Work, Energy and PowerWork and Efficiency of Machines Easy Question 68 of 71 in Work, Energy and Power

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 3 m, the efficiency of pulley system will be : -

A 25%
B 33.3%
C 75%
D 90%

The answer is C.

Solution

Efficiency $\eta = \dfrac{\text{useful work}}{\text{total work}} = \dfrac{mgh}{F \times d}$
Useful work $= 75 \times 10 \times 3 = 2250$ J (taking g = 10 m/s$^2$)
Total work done by the effort $= 250 \times 12 = 3000$ J
$\eta = \dfrac{2250}{3000} = 0.75 = 75$ percent

Concept Efficiency of a pulley system

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71 questions from this chapter have appeared across 27 exam years.