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MHT CET · Physics · Rotational Motion

A disc of radius \(R\) and thickness \(\frac{R}{6}\) has a moment of inertia \(I\) about an axis passing through its centre and perpendicular to its plane. The disc is melted and recast into a solid sphere. The moment of inertia of a sphere about its diameter is

  1. A I5
  2. B I6
  3. C I32
  4. D I64
Verified Solution

Answer & Solution

Correct Answer

(A) I5

Step-by-step Solution

Detailed explanation

Volume of disc is A.d =π.R2×R6=R3×π6 
Moment of inertia of disc is I=12MR2
When the disk is remolded in solid sphere of volume V having radius r, then
πR36=43×πr3R36×34=r3
r3=R38r=R2
Moment of inertia of sphere is given by 25 M.r2=25×M.R24=MR210=MR22×15=I5
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