JEE Main & Advanced Sample Paper JEE Main - Mock Test - 20

  • question_answer
    Three identical spherical shells, each of mass m and radius rare placed as shown in figure. Consider an axis XX? which is touching to two shells and passing through diameter of third shell. Moment of inertia of the system consisting of these three spherical shells about XX? axis is

    A) \[\frac{16}{5}m{{r}^{2}}\]     

    B) \[4m{{r}^{2}}\]

    C) \[\frac{11}{5}m{{r}^{2}}\]     

    D) \[3m{{r}^{2}}\]

    Correct Answer: B

    Solution :

    [b]: Net moment of inertia of the system, \[I={{I}_{1}}+{{I}_{2}}+{{I}_{3}}\] The moment of inertia of a shell about its diameter,\[{{I}_{1}}=\frac{2}{3}m{{r}^{2}}\] The moment of inertia of a shell about its tangent is given by \[{{I}_{2}}={{I}_{3}}={{I}_{1}}+m{{r}^{2}}=\frac{2}{3}m{{r}^{2}}+m{{r}^{2}}=\frac{5}{3}m{{r}^{2}}\] \[\therefore \]\[I=2\times \frac{5}{3}m{{r}^{2}}+\frac{2}{3}m{{r}^{2}}=\frac{12m{{r}^{2}}}{3}=4m{{r}^{2}}\]


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