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Moment of inertia of a uniform circular disc about a diameter is I. Its moment of inertia about an axis ⊥ to its plane and passing through a point on its rim will be

1. 5 I
2. 3 I
3. 6 I
4. 4 I

Correct answer: 6 I

Solution

Using the perpendicular axis theorem, the moment of inertia of the disc about an axis perpendicular to its plane through the center is 2I. Using the parallel axis theorem, the moment of inertia about an axis perpendicular to the plane and passing through the rim is 2I + MR², which simplifies to 6I (since MR² = 4I).

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