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JEE Mains · Physics · STD 11 - System of particles and rotational motion
  • JEE Mains 2020
  • Hard
  • MCQ

The linear mass density of a thin rod \(A B\) of length \(L\) varies from \(A\) to \(B\) as \(\lambda( x )=\lambda_{0}\left(1+\frac{ x }{ L }\right),\) where \(x\) is the distance from A. If \(M\) is the mass of the rod then its moment of inertia about an axis passing through \(A\) and perpendicular to the rod is\(......ML^{2}\)

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Answer & Solution

Correct Answer

(D) \(0.388\)

Step-by-step Solution

Detailed explanation

\(I =\int r ^{2} dm =\int x ^{2} \lambda dx\)

\(I =\int_{0}^{ L } x ^{2} \lambda_{0}\left(1+\frac{ x }{ L }\right) dx\)

\(I=\lambda_{0} \int_{0}^{L}\left(x^{2}+\frac{x^{3}}{L}\right) d x\)

\(I=\lambda\left[\frac{L^{3}}{3}+\frac{L^{3}}{4}\right]\)

\(I =\frac{7 L ^{3} \lambda_{0}}{12}\) \(...(i)\)

\(M=\int_{0}^{L} \lambda \cdot d x=\int_{0}^{L} \lambda_{0}\left(1+\frac{ x }{ L }\right) dx\)

\(M=\lambda_{0}\left(L+\frac{L}{2}\right)=\lambda_{0} \frac{3 L}{2}\)

\(\frac{2}{3} M =\left(\lambda_{0} L \right)\)\(...(ii)\)

\(From\) \((i)\) \(\&\) \((ii)\)

.\(I=\frac{7}{12}\left(\frac{2}{3} M\right) L^{2}=\frac{7 M L^{2}}{18}\)

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