Two masses M and m (with M > m) are connected by means of a pulley as shown in the figure. The system is released from rest. At the instant when mass M has fallen through a distance h, the velocity of mass m will be
√2gh(M−m)(M+m)
If mass m falls through a distance h, mass m rises up through the same distance h. Let v be the common velocity of the masses when this happens.
Now, Loss in PE = Gain in KE
⇒Mgh−mgh=12(M+m)v2
⇒v=√2gh(M−m)(M+m)
Hence, the correct choice is (c).