Question

A boy of mass M is applying a horizontal force to slide a box of mass M' on a rough horizontal surface. The coefficient of friction between the shoes of the boy and the floor is μ'and that between the box and the floor is μ'. In which of the following cases it is certainly not possible to slide the box ?

(a) μ < μ', M < M'

(b) μ >μ', M < M'

(c) μ < μ', M > M'

(d) μ > μ', M> M'.

Answer 1

The correct answer is (a) μ < μ', M < M'

Explanation:

The force applied by the boy on the box is equal to the force of friction between the shoes of the boy and the floor which is equal to µMg.

Force of friction between the box and the floor = µ'M'g.

To slide the box µMg>µ'M'g

→ µM>µ'M' This is not possible only if µ<µ', M<M'