Identify the correct statement about work energy theorem.

Options

A. Work done by all the forces is equal to the decrease in potential energy.
B. Work done by all the forces except the conservative is equal to the change in mechanical energy.
C. Work done by all the forces is equal to the change in kinetic energy .
D. Work done by all the forces is equal to the change in potential energy

Explanation

To solve the question, we need to analyze the statements provided about the work-energy theorem and identify which one is correct.

### Step-by-Step Solution:

1. **Understanding the Work-Energy Theorem**:
The work-energy theorem states that the work done by the net force acting on an object is equal to the change in its kinetic energy. Mathematically, this can be expressed as:
\[ W = \Delta KE = KE_f - KE_i \]
where \( W \) is the work done, \( KE_f \) is the final kinetic energy, and \( KE_i \) is the initial kinetic energy.

2. **Analyzing the Statements**:
Let's evaluate each statement provided in the question:
- **Statement 1**: Work done by all the forces is equal to decrease in potential energy.
- This statement is not correct because the work done by forces is not solely related to potential energy.
- **Statement 2**: Work done by all the forces except the conservative is equal to change in mechanical energy.
- This statement is also incorrect. The work done by non-conservative forces does affect mechanical energy, but it is not simply equal to the change in mechanical energy.
- **Statement 3**: Work done by all the forces is equal to change in kinetic energy.
- This statement is correct as it directly reflects the work-energy theorem.
- **Statement 4**: Work done by all the forces is equal to the change in potential energy.
- This statement is incorrect because work done is not solely equal to the change in potential energy.

3. **Conclusion**:
After evaluating all the statements, we conclude that the correct statement about the work-energy theorem is:
- **Work done by all the forces is equal to change in kinetic energy.**

### Final Answer:
The correct statement about the work-energy theorem is: **Work done by all the forces is equal to change in kinetic energy.**

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