Q: A person pulls a bucket of water from a wall of depth *h*. If the mass of uniform rope is *m* and that of the bucket full of water is *M*, then work done by the person is

(a) $ \displaystyle (M + \frac{m}{2})gh $

(b) $ \displaystyle \frac{1}{2}(M + m)gh $

(c) $\displaystyle (M + )gh $

(d) $ \displaystyle ( \frac{M}{2}+ m)gh $

Ans: (a)

Sol: Center of mass of the rope is at depth h/2 .

Work done= Gain in P.E

$= m g \frac{h}{2} + Mgh $