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 ?
1
µ < µ′ , M < M ′
2
µ > µ′ , M < M ′
3
µ < µ′ , M > M ′
4
µ > µ′ , M > M ′.