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