Blocks shown in figure moves with constant velocity 10 m/s towards right. All surgaces in contact are rough. The friction force applied by B on A is :-

Options

A. 0 N
B. 20 N
C. 10 N
D. insufficient data

Answer

To solve the problem of finding the friction force applied by block B on block A, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Given Information**:
- Blocks are moving with a constant velocity of 10 m/s towards the right.
- All surfaces in contact are rough.
- We need to find the friction force applied by block B on block A.

2. **Identify Key Concepts**:
- Since the blocks are moving with a constant velocity, this implies that there is no acceleration. According to Newton's first law, if the velocity is constant, the net force acting on the blocks is zero.

3. **Apply Newton's Second Law**:
- According to Newton's second law, \( F = ma \), where \( F \) is the net force, \( m \) is the mass, and \( a \) is the acceleration.
- In this case, since the blocks are moving at a constant velocity, the acceleration \( a = 0 \).

4. **Calculate the Net Force**:
- Since \( a = 0 \), we can write:
\[ F = m \cdot 0 = 0 \]
- This means the net force acting on block A is zero.

5. **Analyze the Forces**:
- The only horizontal forces acting on block A are the friction force exerted by block B and any other external forces (if any). However, since the blocks are moving with constant velocity, the friction force must balance any other forces acting on block A.

6. **Conclusion**:
- Since the net force is zero and there is no acceleration, the friction force applied by block B on block A must also be zero. Therefore, the friction force \( F_{friction} = 0 \, \text{N} \).

### Final Answer:
The friction force applied by B on A is **0 N**.