Two blocks of masses'm' and 'M' are arranged as shown in the figure. The coefficient of friction between the two blocks is ' `mu` ', where as between the lower block and the horizontal surface is zero. Find the force 'F' to be applied on the upper block, for the system to be under equilibrium ?

Explanation

On the upper block,
`F = T + f = T + muN`
`F = T + mug`….(1)
On the lower block
`T = mu mg`…….(2)
from (1) and (2), we get, `F = 2mu mg`