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Let the moment of inertia of a hollow cylinder of length 30 cm (inner radius 10 cm and outer radius 20 cm), about its axis be I. The radius of a thin cylinder of the same mass such that its moment of inertia about its axis is also I, is :

1. 16 cm
2. 12 cm
3. 14 cm
4. 18 cm

Correct answer: 16 cm

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