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JEE Main 2017 (9 Apr, Shift 1) · Moment of Inertia & Radius of Gyration

Moment of Inertia & Radius of Gyration question from JEE Main 2017 (9 Apr, Shift 1)

Q172JEE Main 2017 · 9 APR · SHIFT 1Medium

Moment of Inertia & Radius of Gyration

A circular hole of radius R4\frac{R}{4} is made in a thin uniform disc having mass M and radius R, as shown in figure. The moment of inertia of the remaining portion of the disc about an axis passing through the point O and perpendicular to the plane of the disc is:

Figure

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Answer: (b)

  1. Hole mass =M16= \frac{M}{16}, centre at 3R4\frac{3R}{4}.
  2. Ihole=12M16R216+M169R216=19MR2512I_{hole} = \frac{1}{2}\frac{M}{16}\frac{R^2}{16} + \frac{M}{16}\frac{9R^2}{16} = \frac{19MR^2}{512}
  3. I=256MR2512−19MR2512=237MR2512I = \frac{256MR^2}{512} - \frac{19MR^2}{512} = \frac{237MR^2}{512}
  4. So the answer is (b).
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