Moment of inertia of a thin spherical shell of mass M and radius R about a diameter is

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UPPSC AE Mechanical 2022 Official Paper I (Held on 29 May 2022)
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  1. \(\frac{2}{5}\) MR2
  2. \(\frac{4}{5}\) MR2
  3. \(\frac{2}{3}\) MR2
  4. \(\frac{3}{5}\) MR2

Answer (Detailed Solution Below)

Option 3 : \(\frac{2}{3}\) MR2
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Concept:

Moment of inertia:

A moment of inertia is a measure of the resistance of a body to angular acceleration about a given axis that is equal to the sum of the products of each element of mass in the body and the square of the element’s distance from the axis.

I = ∑( m1r1+ m2r22 + m3r32 +m4r42 + …….. + mnrn2)

Moment of inertia of a thin spherical shell of mass M and radius R about its diameter.

\({\rm{I}} = \frac{2}{3}{\rm{M}}{{\rm{R}}^2}\)

  • For a rigid body system, the moment of inertia is the sum of the moments of inertia of all its particles taken about the same axis.

F2 J.K 8.7.20 Pallavi D10

\(I=\sum m_{i}{r_{i}}^{2}\)

where I is the Moment of Inertia, m is point mass, r is the perpendicular distance from the axis of rotation.

The moment of inertia of different bodies is given in the below table:

Shape Axis of rotation Moment of inertia
Ring axis passing through the center perpendicular to the plane of the ring \(I = mr^2\)
Ring axis passing through the diameter of the ring \(I = {1 \over 2}mr^2\)
Solid Cylinder axis passing through the center perpendicular to the plane of the ring \(I = {1 \over 2}mr^2\)
Solid sphere through center \(I = {2 \over 5}mr^2\)
Hollow sphere through center \(I = {2 \over 3}mr^2\)
Rod  through midpoint perpendicular to the rod \(I = {1 \over 12}ml^2\)
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