Q.

A cubical block of side L rests on a rough horizontal surface with coefficient of friction μ. A horizontal force F is applied on the block as shown. If the coefficient of friction is sufficiently high so that the block does not slide before toppling, the minimum force required to topple the block is                       [2000]

1 infinitesimal  
2 mg4  
3 mg2  
4 mg(1-μ)  

Ans.

(3)

Here, due to applied force normal reaction shifts to one corner. At this situation, the cubical block starts toppling about point O. About point O torque

F×L=mg×L2  F=mg2

Hence minimum force required to topple the block,

F=mg2