In the arrangement shown in the figure, the ends \(P\) & \(Q\) of an inextensible spring move downwards with a uniform speed \(u\). Pulleys \(A\) & \(B\) are fixed. The mass \(m\) moves upwards with a speed of
Demasking the problem:
This problem is quite famous. It appeared in IIT-JEE 1982, NSEP 2003 & is also present in the exercises of a good physics book.