Assertion `:-` Work done is positive when force acts in the direction of displacement.
Reason `:-` Work done by frictional force can not be positive.

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion.
B. If both Assertion & Reason are True but Reason is not a correct explanation of the Assertiion.
C. If Assertion is True but the Reason is False.
D. If both Assertion & Reason are False

Answer

To analyze the assertion and reason provided in the question, we can break down the concepts of work done, force, and displacement step by step.

### Step-by-Step Solution:

1. **Understanding Work Done**:
- Work done (W) by a force is defined as the dot product of the force (F) and the displacement (S) of the object. Mathematically, it can be expressed as:
\[ W = \vec{F} \cdot \vec{S} = F \cdot S \cdot \cos(\theta) \]
- Here, \(\theta\) is the angle between the force vector and the displacement vector.

2. **Positive Work Done**:
- Work done is considered positive when the force acts in the same direction as the displacement. This occurs when \(\theta = 0^\circ\), leading to:
\[ W = F \cdot S \cdot \cos(0) = F \cdot S \cdot 1 = F \cdot S \]
- Therefore, the assertion that "Work done is positive when force acts in the direction of displacement" is **true**.

3. **Frictional Force and Work Done**:
- The reason states that "Work done by frictional force cannot be positive."
- Frictional force typically acts opposite to the direction of displacement. When an object moves, the frictional force does negative work because it opposes the motion. This can be expressed as:
\[ W_{\text{friction}} = F_{\text{friction}} \cdot S \cdot \cos(180^\circ) = -F_{\text{friction}} \cdot S \]
- Thus, the work done by friction is negative when it opposes the motion.

4. **Counterexamples**:
- However, there are scenarios where friction can do positive work. For example, when a car accelerates, the frictional force between the tires and the road acts in the direction of the car's displacement, contributing positively to the car's acceleration.
- Hence, the statement that "Work done by frictional force cannot be positive" is **false**.

5. **Conclusion**:
- The assertion is true, while the reason is false. Therefore, the overall conclusion is that the assertion is correct, but the reason provided is incorrect.

### Final Answer:
- Assertion: True
- Reason: False