Moment of Inertia Calculation Assumption – Rankers Physics

Moment of Inertia: Practice Problem & Solution

Assertion (A): For the purpose of calculation of moment of inertia, body's mass can be assumed to be concentrated at its centre of mass. Reason (R): Moment of inertia of a rigid about an axis passing through its centre of mass is zero.  
Both (A) & (R) are true and the (R) is the correct explanation of the (A)
Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
(A) is true but (R) is false
Both (A) and (R) are false

Solution Explained:

To solve this problem, we apply the core principles of Moment of Inertia. Understanding the underlying formula is key to arriving at the correct answer below:

Moment of inertia depends critically on the distribution of mass relative to the axis of rotation, so mass cannot generally be assumed concentrated at the center of mass (A is false). Also, the moment of inertia of a rigid body about an axis passing through its center of mass is generally not zero (e.g., a disc has \(I = \frac{1}{2}MR^2\)). Thus, (R) is false. Both statements are incorrect.

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