A solid sphere of radius R has moment of inertia I about its geometrical axis. It is melted into a disc of radius r and thickness t. If its moment of inertia about the tangential axis (which is perpendicular to plane of the disc), is also equal to I, then the value of r is equal to

Question

A solid sphere of radius R has moment of inertia I about its geometrical axis. It is melted into a disc of radius r and thickness t. If its moment of inertia about the tangential axis (which is perpendicular to plane of the disc), is also equal to I, then the value of r is equal to, 2 1 5 R, 2 5 R, 3 15 R, 3 15 R

MARKS App · Accepted Answer

2 5 MR 2 = 1 2 Mr 2 + Mr 2 ⇒ 2 5 MR 2 = 3 2 Mr 2 ⇒ r = 2 1 5 R

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