In the arrangement shown in the 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

Options

A. `2 U cos theta`
B. `U// cos theta`
C. `2U // cos theta`
D. `U cos theta

Answer

B

Explanation

Let the velocity of the block m be v upwards, then `v cos theta = u implies v = U // cos theta`