A block of mass M is held against a rough vertical wall by pressing it with a finger . If the coefficient of friction between the block and the wall is `mu` and the acceleration due to gravity is g , calculate the minimum force required to be applied by the finger to hold the block against the wall.

Explanation

Let `F` be the force applied by the finger on the block `N` is normal reaction of the wall on the block `Mg` is weight of block acting vertically downwards. `F` is the force of friction between the wall and the block which acts upwards as shown in
The block will not fall, if `f = mg `
` mu N = mg , or mu F = mg , or F = (Mg)/(mu) `
.