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

To solve the problem of finding the minimum force required to hold a block of mass \( M \) against a rough vertical wall, we can follow these steps:

### Step 1: Identify the Forces Acting on the Block
- The block experiences several forces:
1. The gravitational force acting downward, which is \( mg \) (where \( m \) is the mass of the block and \( g \) is the acceleration due to gravity).
2. The normal force \( N \) exerted by the wall on the block, acting horizontally.
3. The force \( F \) applied by the finger, acting horizontally against the wall.
4. The frictional force \( f \) acting upward, which opposes the downward gravitational force.
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