Assertion : When pendulum bob is rotating in a circle around the point of suspension then work done by tension and the weight is zero .
Reason : Work done by a force is defined as dot product of force vector and displacement vector .

Options

A. If both assertion and reason are corret and reason is a correct explanation of the assertion .
B. If both assertion and reason are correct but reason is ot the correct explanation of assertion .
C. If assertion is correct but reason is incorrect .
D. If assertion is incorrect and reason is incorrect .

Explanation

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

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that when a pendulum bob is rotating in a circle around the point of suspension, the work done by tension and weight is zero.
- To evaluate this, we need to consider the forces acting on the pendulum bob.

2. **Analyzing the Work Done by Tension**:
- The tension in the string acts towards the center of the circle (centripetal force).
- The displacement of the bob is tangential to the circle at any point.
- The angle between the tension (radial direction) and the displacement (tangential direction) is 90 degrees.
- Work done (W) is given by the formula:
\[ W = F \cdot d = F \cdot ds \cdot \cos(\theta) \]
- Since \(\theta = 90^\circ\), \(\cos(90^\circ) = 0\).
- Therefore, the work done by tension is:
\[ W_{\text{tension}} = F_{\text{tension}} \cdot ds \cdot 0 = 0 \]

3. **Analyzing the Work Done by Weight**:
- The weight of the bob (mg) acts vertically downward.
- The displacement of the bob during its circular motion is tangential to the circle.
- At different points in the circular path, the angle between the weight and the displacement changes.
- Thus, the work done by weight is not zero because there are points where the angle is not 90 degrees, and hence:
\[ W_{\text{weight}} \neq 0 \]

4. **Conclusion about the Assertion**:
- Since the work done by tension is zero but the work done by weight is not zero, the assertion is incorrect.

5. **Understanding the Reason**:
- The reason states that work done by a force is defined as the dot product of the force vector and the displacement vector.
- This definition is correct, as it aligns with the formula for work done.
- Therefore, the reason is correct.

6. **Final Evaluation**:
- The assertion is incorrect, and the reason is correct.
- According to the options provided, the correct choice is that the assertion is incorrect and the reason is correct.

### Final Answer:
The assertion is incorrect, and the reason is correct.