A block of mass 0.1 is held against a wall applying a horizontal force of 5N on block. If the coefficient of friction between the block and the wall is 0.5, the magnitude of the frictional force acting on the block is:

Options

A. 2.5 N
B. 0.98 N
C. 4.9 N
D. 0.49 N

Explanation

To solve the problem, we need to find the magnitude of the frictional force acting on a block of mass 0.1 kg that is held against a wall with a horizontal force of 5 N applied to it. The coefficient of friction between the block and the wall is 0.5.

### Step-by-Step Solution:

1. **Identify the Forces Acting on the Block:**
- The block experiences a horizontal force \( F = 5 \, \text{N} \) applied against the wall.
- The weight of the block \( W = mg \), where \( m = 0.1 \, \text{kg} \) and \( g = 9.8 \, \text{m/s}^2 \).
- The normal force \( N \) exerted by the wall on the block.
- The frictional force \( f \) acting opposite to the direction of the applied force.

2. **Calculate the Weight of the Block:**
\[ W = mg = 0.1 \, \text{kg} \times 9.8 \, \text{m/s}^2 = 0.98 \, \text{N} \]

3. **Determine the Maximum Static Friction Force:**
The maximum static friction force \( f_s^{\text{max}} \) can be calculated using the formula:
\[ f_s^{\text{max}} = \mu_s N \]
where \( \mu_s = 0.5 \) is the coefficient of friction.

4. **Calculate the Normal Force:**
Since the block is in equilibrium vertically, the normal force \( N \) is equal to the weight of the block:
\[ N = W = 0.98 \, \text{N} \]

5. **Calculate the Maximum Static Friction Force:**
\[ f_s^{\text{max}} = \mu_s N = 0.5 \times 0.98 \, \text{N} = 0.49 \, \text{N} \]

6. **Determine the Frictional Force:**
The frictional force \( f \) will adjust to prevent the block from sliding down. Since the applied force \( F = 5 \, \text{N} \) is greater than the maximum static friction force \( f_s^{\text{max}} = 0.49 \, \text{N} \), the frictional force will be equal to its maximum value:
\[ f = f_s^{\text{max}} = 0.49 \, \text{N} \]

### Final Answer:
The magnitude of the frictional force acting on the block is \( 0.49 \, \text{N} \).