A : The change in kinetic energy of a particle is equal to the work done on it by the net force.
R : The work-energy theorem can be used only in conservative field.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark (1).
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark (2).
C. If Assertion is true statement but Reason is false, then mark (3).
D. If both Assertion and Reason are falsė statements, then mark (4).

Answer

To solve the problem, we need to analyze the assertion and the reason given in the question.

**Assertion (A):** The change in kinetic energy of a particle is equal to the work done on it by the net force.
**Reason (R):** The work-energy theorem can be used only in conservative fields.

### Step-by-step Solution:

1. **Understanding the Assertion (A):**
- The assertion states that the change in kinetic energy of a particle is equal to the work done on it by the net force. This is a statement of the work-energy theorem, which is a fundamental principle in physics.
- Mathematically, this can be expressed as:
\[ \Delta KE = W_{net} \]
where \(\Delta KE\) is the change in kinetic energy and \(W_{net}\) is the work done by the net force.

2. **Evaluating the Reason (R):**
- The reason states that the work-energy theorem can be used only in conservative fields. This is not entirely accurate.
- The work-energy theorem applies to both conservative and non-conservative forces. It states that the total work done on an object (which can include work done by non-conservative forces) results in a change in kinetic energy.

3. **Conclusion:**
- Since the assertion is true (the change in kinetic energy is indeed equal to the work done by the net force), but the reason provided is not a correct explanation of the assertion (as the work-energy theorem applies in both conservative and non-conservative fields), we conclude:
- Both the assertion and the reason are true, but the reason is not the correct explanation for the assertion.

4. **Final Answer:**
- The correct option is that the assertion is true, and the reason is true but not the correct explanation of the assertion.