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MHT CET 2026 (17 Apr, Shift 1) · Moment of Inertia & Radius of Gyration

Moment of Inertia & Radius of Gyration question from MHT CET 2026 (17 Apr, Shift 1)

Q13MHT CET 2026 · 17 APR · SHIFT 1Medium

Moment of Inertia & Radius of Gyration

A system of five solid spheres each of mass ' $m$ ' and radius ' $r$ ' are rotating about an axis AA' as shown in figure. Hence the moment of inertia of the system about the axis of rotation AA' is

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Answer: (c)

Three spheres have AA' as a diameter: $3\times\frac{2}{5}mr^2 = \frac{6}{5}mr^2$ .
Two side spheres touch the axis ( $d = r$ ): $2\left(\frac{2}{5}mr^2 + mr^2\right) = \frac{14}{5}mr^2$ .
$I = \frac{20}{5}mr^2 = 4mr^2$ , so the answer is (c).

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