Medium MCQ +4 / -1 PYQ · JEE Mains 2020

Consider two uniform discs of the same thickness and different radii R1 = R and
R2 = $\alpha$R made of the same material. If the ratio of their moments of inertia I1 and I2 , respectively, about their axes is I1 : I2 = 1 : 16 then the value of $\alpha$ is :

  1. A $\sqrt 2$
  2. B 2 Correct answer
  3. C $2\sqrt 2$
  4. D 4

Solution

Moment of inertia of disc, $$I = {{M{R^2}} \over 2} = {{\left[ {p\left( {\pi {R^2}} \right)t} \right]{R^2}} \over 2}$$<br><br>$I = K{R^4}$<br><br>${{{I_1}} \over {{I_2}}} = {\left( {{{{R_1}} \over {{R_2}}}} \right)^4}$<br><br>$${1 \over {16}} = {\left( {{R \over {\alpha R}}} \right)^4} \Rightarrow \alpha = {\left( {16} \right)^{{1 \over 4}}} = 2$$

About this question

Subject: Physics · Chapter: Rotational Motion · Topic: Centre of Mass

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