Analogue of mass in rotational motion is.

Options

A. moment of inertia
B. torque
C. radius of gyration
D. angular momentum

Explanation

To determine the analogue of mass in rotational motion, we need to understand the role of mass in linear motion and how it translates to rotational dynamics.

### Step-by-Step Solution:

1. **Understanding Mass in Linear Motion**:
- In linear motion, mass (m) is a measure of an object's resistance to acceleration when a force is applied. It is a scalar quantity and plays a crucial role in Newton's second law of motion (F = ma).

2. **Transitioning to Rotational Motion**:
- In rotational motion, we need a similar quantity that describes how an object resists changes to its rotational state when a torque is applied.

3. **Identifying the Correct Term**:
- The term that serves this purpose in rotational motion is called the **moment of inertia (I)**. It quantifies how mass is distributed relative to the axis of rotation and affects how much torque is needed for a desired angular acceleration.

4. **Comparing Options**:
- Let's analyze the options given:
- **Inertia**: This is a general term that refers to the property of matter to resist changes in motion, but in the context of rotational motion, it specifically refers to moment of inertia.
- **Torque**: This is the rotational analogue of force, not mass.
- **Radius of Gyration**: This is a measure related to the distribution of mass but is not the analogue of mass itself.
- **Angular Momentum**: This is a measure of the quantity of rotation of an object but is not analogous to mass.

5. **Conclusion**:
- Therefore, the analogue of mass in rotational motion is **moment of inertia (I)**.

### Final Answer:
The analogue of mass in rotational motion is **moment of inertia (I)**.

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