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

Asked in AIPMT 2001 · Pulleys with inclines and movable pulleys

• (1) 25%
• (2) 33.3%
• (3) 75%
• (4) 90%

Step-by-step solution

Why the other options are wrong

• (1) This is the reciprocal of the distance ratio, 3/12, mistaken for the efficiency; the forces have to come into it as well.
• (2) Comes from comparing the two forces alone, 250/750, without the distances.
• (4) Does not follow from these numbers; the useful work is 2250 J out of 3000 J supplied.

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