Analogue of mass in rotational motion is

Options

A. moment of inertia
B. angular momentum
C. gyration
D. None of these

Explanation

To solve the question regarding the analogue of mass in rotational motion, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Concept of Mass in Linear Motion**:
- In linear motion, mass (m) is a measure of an object's resistance to acceleration when a force is applied. The relationship is given by Newton's second law:
\[ F = m \cdot a \]
- Here, \( F \) is the force, \( m \) is the mass, and \( a \) is the linear acceleration.

2. **Identifying the Need for an Analogue in Rotational Motion**:
- In rotational motion, we need a similar quantity that describes how an object resists angular acceleration when a torque is applied.

3. **Defining Moment of Inertia**:
- The analogue of mass in rotational motion is called the moment of inertia (I). It is defined as:
\[ I = \sum m_i \cdot r_i^2 \]
- Where \( m_i \) is the mass of each point mass in the body and \( r_i \) is the distance of that mass from the axis of rotation.

4. **Relating Moment of Inertia to Torque and Angular Acceleration**:
- In rotational motion, the relationship between torque (\( \tau \)), moment of inertia (\( I \)), and angular acceleration (\( \alpha \)) is given by:
\[ \tau = I \cdot \alpha \]
- This equation is analogous to the linear motion equation \( F = m \cdot a \).

5. **Conclusion**:
- Since the moment of inertia plays a role in rotational motion similar to that of mass in linear motion, we conclude that the correct answer to the question is:
\[ \text{Moment of Inertia (I)} \]

### Final Answer:
The analogue of mass in rotational motion is **Moment of Inertia**.

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