Question

A cubical block of side length L rests on a rough horizontal surface having the 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

(a) infinitesimal 

(b) mg/4

(c) mg/2

(d) mg(1 -  μ)

Answer 1

Correct Answer is: (c) mg/2

When F is applied, the normal reaction (N) of the floor moves to the right. The cube topples when N reaches its edge.

Here, N = mg and the force of friction = f = F. 

Taking torque about the centre C,

F x L/2 + f x L/2 = N x L/2

or 2F = mg.