Select the correct alternative.

Options

A. Work done by kinetic friction on a body always results in a loss of its kinetic energy.
B. Work done on a body, in the motion of that body over a close loop is zero for every force in nature.
C. Total mechanical energy of a system is always conserved no matter what type of internal and external forces on the body are present.
D. When total work done by a conservetive force on the system is positive then the potential energy associated with this force decreses.

Explanation

To solve the question, we need to analyze each of the given options regarding work done by forces and the conservation of energy principles.

### Step-by-Step Solution:

1. **Understanding Work Done by Kinetic Friction**:
- Kinetic friction always opposes the motion of the body. Therefore, the work done by kinetic friction is negative, which results in a loss of kinetic energy of the body.
- **Conclusion**: Option 1 is incorrect.

2. **Work Done by Kinetic Energy**:
- The statement suggests that the work done by kinetic energy on a body may increase its kinetic energy. However, work done on a body can either increase or decrease its kinetic energy depending on the direction of the force applied.
- **Conclusion**: Option 2 is not always correct.

3. **Total Mechanical Energy Conservation**:
- The total mechanical energy of a system is conserved only when the net work done by external forces is zero and internal forces are conservative. If non-conservative forces (like friction) do work, the mechanical energy is not conserved.
- **Conclusion**: Option 3 is incorrect.

4. **Work Done by Conservative Forces**:
- When the total work done by a conservative force is positive, it indicates that energy is being transferred to the kinetic energy of the system, which results in a decrease in potential energy associated with that force.
- **Conclusion**: Option 4 is correct.

### Final Answer:
The correct alternative is **Option 4**.

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