A pulley system can lift a load of 1200 N by an effort of 250 N. If the resistance due to the weight of movable parts and friction is 300 N. Find the total number of pulleys in the system.

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Solution

The correct option is C
6

Given: load = 1200 N, effort = 250 N, and weight of movable pulleys and friction = 300 N.
MA $= \frac{L o a d}{E f f o r t} = \frac{1200}{250} = 4.8$

Velocity ratio, VR = Ideal mechanical advantage
$= \frac{T o t a l r e s i s t a n c e o v e r c o m e}{E f f o r t}$
$= \frac{U s e f u l l o a d + o t h e r f o r c e}{E f f o r t}$
$= \frac{1200 + 300}{250} = \frac{1500}{250} = 6$

Total number of pulleys = VR = 6

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