A horizontal force of 10 N is necessary to just hold a block stationary against a wall. The coefficient of friction between the block and the wall is 0.2. The weight of the block is

The correct answer is 2 N.

Let us carefully understand the physical setup before solving.

Understanding the Setup:
A block is pressed horizontally against a vertical wall by a horizontal force. The block remains stationary — it does not slide down. We need to find the weight of the block.

Step 1: Identify all forces acting on the block.

There are four forces at play:
1. Applied horizontal force (F) — pushes the block into the wall. F = 10 N (acting horizontally, into the wall).
2. Normal reaction (N) — the wall pushes back on the block horizontally (outward). By Newton's third law, N = F = 10 N.
3. Weight (W) — acts vertically downward.
4. Friction force (f) — acts vertically upward along the wall surface, preventing the block from sliding down.

Step 2: Apply the condition for equilibrium in the horizontal direction.

Since the block does not move horizontally:

N=F=10\text{N}

Step 3: Calculate the maximum static friction force.

The friction force is given by:

f=\mu \times N

where \mu is the coefficient of friction = 0.2

f=0.2\times 10=2\text{N}

Step 4: Apply the condition for equilibrium in the vertical direction.

Since the block is "just held stationary" (on the verge of sliding), the friction force exactly balances the weight of the block:

f=W

W=2\text{N}

Key Insight:
Notice that the horizontal applied force does NOT directly support the weight. Its role is to create a normal force on the wall, which in turn generates a friction force that acts vertically upward to counteract the downward weight. This is why the weight equals the friction force, not the applied force itself.

Therefore, the weight of the block is 2 N.