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JEE Main 2020 (4 Sep, Shift 2) · Moment of Inertia & Radius of Gyration

Moment of Inertia & Radius of Gyration question from JEE Main 2020 (4 Sep, Shift 2)

Q147JEE Main 2020 · 4 SEP · SHIFT 2Medium

Moment of Inertia & Radius of Gyration

For a uniform rectangular sheet shown in the figure, the ratio of moments of inertia about the axes perpendicular to the sheet and passing through O (the centre of mass) and O' (corner point) is:

Figure

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Answer: (b)

  1. Through centre O: IO=M12(a2+b2)I_O = \frac{M}{12}(a^2 + b^2).
  2. O' is a corner, at distance 12a2+b2\frac{1}{2}\sqrt{a^2 + b^2} from O: IO′=M12(a2+b2)+M4(a2+b2)=M3(a2+b2)I_{O'} = \frac{M}{12}(a^2+b^2) + \frac{M}{4}(a^2+b^2) = \frac{M}{3}(a^2+b^2).
  3. IOIO′=1/121/3=14\frac{I_O}{I_{O'}} = \frac{1/12}{1/3} = \frac{1}{4}
  4. So the answer is (b) 14\frac{1}{4}.
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