Which of the following statement is not true ?

Options

A. Work done by conservative force on an object depends only on the initial and final states and not on the path taken.
B. The change in the potential energy of a system corresponding to conservative internal forces is equals negative of the work done by these forces.
C. If some of the internal forces within a system are non`-` conservative , then the mechanical energy of the system is not constant.
D. If the internal forces are conservative,the work donw by the internal forces is equal to the change in mechanical energy.

Answer

To solve the question, we need to analyze each statement provided and determine which one is not true.

### Step-by-Step Solution:

1. **Understanding Conservative Forces**:
- Conservative forces are those for which the work done is independent of the path taken and depends only on the initial and final positions.
- Example: Gravitational force is a conservative force.

2. **Analyzing Statement 1**:
- "The work done by conservative forces on an object depends only upon initial and final state."
- This statement is true because the work done by conservative forces (like gravity) depends only on the height difference, not the path taken.

3. **Analyzing Statement 2**:
- "The change in potential energy of a system corresponding to the conservative internal forces equals the negative of work done."
- This statement is also true. The work-energy principle states that the work done by conservative forces is equal to the negative change in potential energy.

4. **Analyzing Statement 3**:
- "If some of the internal energy within the system are non-conservative, then the mechanical energy of the system is not constant."
- This statement is true. Non-conservative forces (like friction) do work that can change the mechanical energy of the system.

5. **Analyzing Statement 4**:
- "If internal forces are conservative, then the work done by internal forces equals the change in mechanical energy."
- This statement is not true. The work done by internal conservative forces does not equal the change in mechanical energy; instead, it relates to the change in potential energy.

### Conclusion:
The statement that is not true is the fourth one: "If internal forces are conservative, then the work done by internal forces equals the change in mechanical energy."