Work energy theorem is applicable

Options

A. Only for conservation forces
B. Only for inertial frames
C. Only when pseudo forces are absent
D. Always

Answer

To solve the question regarding the applicability of the work-energy theorem, we will analyze each option provided and determine the correct answer step by step.

### Step 1: Understand the Work-Energy Theorem
The work-energy theorem states that the net work done by the forces acting on an object is equal to the change in its kinetic energy. Mathematically, this can be expressed as:
\[ W_{\text{net}} = \Delta KE \]
where \( W_{\text{net}} \) is the net work done and \( \Delta KE \) is the change in kinetic energy.

**Hint:** Remember that the work-energy theorem relates work done to changes in kinetic energy.

### Step 2: Analyze Each Option
1. **Only for Conservative Forces**: This option suggests that the theorem is only applicable when conservative forces (like gravity) are acting. However, the work-energy theorem is valid for all types of forces, not just conservative ones.

**Hint:** Consider whether non-conservative forces (like friction) affect the validity of the theorem.

2. **Only for Inertial Frames**: The theorem is indeed most straightforwardly applied in inertial frames, where Newton's laws hold without modification. However, it can also be applied in non-inertial frames with the inclusion of pseudo forces.

**Hint:** Think about how forces are perceived differently in inertial vs. non-inertial frames.

3. **Only When Pseudo Forces are Absent**: This option implies that the theorem cannot be used when pseudo forces are present. This is incorrect, as the theorem can still be applied in non-inertial frames by accounting for pseudo forces.

**Hint:** Reflect on how pseudo forces can be incorporated into the analysis.

4. **Always**: This option states that the work-energy theorem is applicable in all scenarios, regardless of the type of forces or the frame of reference. This is the most accurate statement, as the theorem holds true universally as long as we consider all forces acting on the object.

**Hint:** Consider the general applicability of the theorem across different scenarios.

### Step 3: Conclusion
After analyzing all the options, we find that the work-energy theorem is indeed applicable in all situations, making option D ("always") the correct choice.

### Final Answer
The correct answer is **D: Always**.