Up, Up, and ... Oops!

Classical Mechanics Level 2

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.

Happy Solving!

2u/\cos \theta

2u \cos \theta

u\cos \theta

None of These

u/\cos \theta