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General
Easy
Question
In the arrangement shown in figure the ends P and Q of an unstretchable string move downwards with uniform speed U. Pulleys A and B are fixed. Mass M moves upwards with a speed
The correct answer is:
As P and Q fall down, the length l decreases at the rate of U m/s.
From the figure, 
Differentiating with respect to time
Þ
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