Assertion : Static friction is a self-adjusting force upto its limit `mu_(s)N "where" mu_(s)` is the coefficient of static friction.
Reason: One can use the equation `f_(s)=mu_(s)N` only when the maximum value of static friction comes into play

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true and reason is the not correct explanation of assertion.
C. If assertion is true but reason is false
D. If both assertion and reason are false.

Answer

To solve the question, we need to analyze both the assertion and the reason provided.

### Step 1: Understand the Assertion
The assertion states that "Static friction is a self-adjusting force up to its limit `μ_s N`, where `μ_s` is the coefficient of static friction."

**Explanation:**
- Static friction acts to oppose the relative motion between two surfaces in contact.
- It can adjust its magnitude based on the applied external force, up to a maximum limit.
- The maximum static friction force is given by the formula:
\[ f_s^{max} = \mu_s N \]
where \(N\) is the normal force.

### Step 2: Understand the Reason
The reason states that "One can use the equation `f_s = μ_s N` only when the maximum value of static friction comes into play."

**Explanation:**
- The equation \(f_s = \mu_s N\) applies only when the static friction is at its maximum limit.
- If the applied force is less than this maximum, the static friction force will equal the applied force, not necessarily \(μ_s N\).

### Step 3: Analyze the Relationship Between Assertion and Reason
- Both the assertion and the reason are true.
- The assertion correctly describes the nature of static friction as a self-adjusting force.
- The reason accurately states the condition under which the equation for static friction can be applied.

### Step 4: Determine the Logical Connection
- While both statements are true, the reason does not directly explain why static friction is self-adjusting. It merely states a condition for using the equation.

### Conclusion
- The assertion is true, and the reason is also true, but the reason does not explain the assertion. Therefore, the final answer is:
- **Option B**: Both assertion and reason are true, but the reason is not the correct explanation for the assertion.