Question

In the arrangement shown in fig. 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 .

• A. $2Ucos\theta$
• B. $Ucos\theta$
• C. $2U/cos\theta$
• D. $U/\cos \theta$

Answer 1

The correct option is D $U/\cos \theta$

Since the string is unstretchable the velocity component of every point on string along the length is same, otherwise the string will break.

So the velocity component of block along any string must be equal to $U$

Speed points on the string, $U=v\cos \theta$

$v=\frac{U}{\cos \theta }$