Select the correct alternative (s)

Options

A. Elastic forces are not always conservative
B. Elastic forces are always conservative
C. Elastic forces are-conservative only when Hooke's law is obeyed
D. Elastic forces are not conservative

Answer

To solve the problem, we need to analyze the statements regarding elastic forces and determine which alternatives are correct based on the principles of elasticity and Hooke's law.

### Step-by-Step Solution:

1. **Understanding Elastic Forces**:
- Elastic forces are the forces that restore a deformed object to its original shape. They are typically associated with materials that obey Hooke's law.

2. **Hooke's Law**:
- Hooke's law states that the force exerted by a spring (or elastic material) is directly proportional to the displacement from its equilibrium position, as long as the material is not deformed beyond its elastic limit. Mathematically, it can be expressed as:
\[ F = -kx \]
where \( F \) is the restoring force, \( k \) is the spring constant, and \( x \) is the displacement.

3. **Conservative Forces**:
- A conservative force is one where the work done in moving an object between two points is independent of the path taken. In the case of elastic forces, if the deformation is within the elastic limit, the work done is stored as potential energy and can be fully recovered.

4. **Evaluating the Options**:
- **Option 1**: "Elastic forces are not always conservative."
- This statement is **true**. If the elastic limit is exceeded, the material may undergo permanent deformation, and energy is not fully recoverable.
- **Option 2**: "Elastic forces are always conservative."
- This statement is **false**. Elastic forces are conservative only when the material obeys Hooke's law and remains within its elastic limit.
- **Option 3**: "Elastic forces are conservative only when Hooke's law is obeyed."
- This statement is **true**. As mentioned, elastic forces behave conservatively only within the elastic limit defined by Hooke's law.
- **Option 4**: "Elastic forces are not conservative."
- This statement is **false**. Elastic forces can be conservative when the material is deformed within its elastic limit.

5. **Conclusion**:
- The correct alternatives are:
- "Elastic forces are not always conservative."
- "Elastic forces are conservative only when Hooke's law is obeyed."

### Final Answer:
The correct alternatives are:
1. Elastic forces are not always conservative.
2. Elastic forces are conservative only when Hooke's law is obeyed.