Q.

A string of negligible mass going over a clamped pulley of mass m supports a block of mass M as shown in the figure. The force on the pulley by the clamp is given by     [2001]

1 2Mg  
2 2mg  
3 (M+m)2+m2g  
4 (M+m)2+M2g  

Ans.

(4)

At equilibrium T=Mg

F.B.D. of pulley

F1=(m+M)g

The resultant force on pulley

F=F12+T2=[(m+M)2+M2]g

As pulley is on rest, force applied by clamp should be equal to F and opposite to it.