Question

A system is shown in the figure and man is pulling the rope from both sides with constant speed ${}^{\prime }{u}^{\prime }$. Then the speed of the block will be ($M$ moves vertically):

• A. $\frac{3u}{4}$
• B. $\frac{3u}{2}$
• C. $\frac{u}{4}$
• D. None of these

Answer 1

The correct option is A $\frac{3u}{4}$

Imagine block A and B is being pulled at the speed u instead of man pullling the string at speed $u$.

By Virtual Method,

$\sum T.V=0$

Let the velocity of mass $M$ and $V$ in upward direction

applying the law

$-Tu-\frac{Tu}{2}+2Tv=0$

$v=\frac{3u}{4}$