(A) : When a bicycle is in motion, the force of friction exerted by the ground on the two wheels is always in forward direction.
(R ) : The frictional force only when the bodies are in contact.

Options

A. Both (A) and (R ) are true and (R ) is the correct explanation of (A)
B. Both (A) and (R ) are true and (R ) is not the correct explanation of (A)
C. (A) is true but (R ) is false
D. (A) is false but (R ) is true

Answer

To solve the assertion and reason question, we will analyze both statements step by step.

### Step 1: Analyze the Assertion
**Assertion (A)**: "When a bicycle is in motion, the force of friction exerted by the ground on the two wheels is always in forward direction."

- When a bicycle moves, the rear wheel pushes backward against the ground due to the motion of the bicycle. According to Newton's third law, the ground exerts an equal and opposite force (friction) on the rear wheel, which acts in the forward direction.
- However, the front wheel does not push backward; instead, it rotates forward. The frictional force acting on the front wheel is directed backward to oppose the motion of the bicycle.

**Conclusion**: The assertion is incorrect because the frictional force on the front wheel is not in the forward direction.

### Step 2: Analyze the Reason
**Reason (R)**: "The frictional force acts only when the bodies are in contact."

- This statement is true. Friction is a contact force, meaning it only occurs when two surfaces are in contact with each other.

**Conclusion**: The reason is correct because it accurately describes the nature of friction.

### Final Conclusion
Based on the analysis:
- The assertion is false.
- The reason is true.

Thus, the correct answer is: **Assertion is false, but reason is true.**