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A thin disc of mass M and radius R has mass per unit area σ (r) = kr 2 where r is the distance from its centre. Its moment of inertia about an axis going through its centre of mass and perpendicular to its plane is :

1. 3 MR 2 2
2. 6 MR 2
3. 3 MR 2
4. 2 MR 2

Correct answer: 3 MR 2 2

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