Chhattisgarh PMT Chhattisgarh PMT Solved Paper-2004

  • question_answer
    Three rings each of mass M and radius R are arranged as shown in the figure. The moment of inertia of the system about YY' will be

    A)  3 MR2                                  

    B)  3/2 MR2

    C)  5 MR2                                  

    D)  7/2 MR2

    Correct Answer: D

    Solution :

    Clearly \[{{I}_{YY'}}={{I}_{1}}({{I}_{2}}+{{I}_{3}})\] where \[{{I}_{1}}=MI\] about diameter \[=\frac{1}{2}M{{R}^{2}}\]and \[{{I}_{2}}={{I}_{3}}=MI\]about tangent                 \[{{I}_{2}}={{I}_{3}}=\frac{1}{2}M{{R}^{2}}+M{{R}^{2}}\] (By parallel axis theorem)                 \[\therefore \]  \[{{I}_{2}}={{I}_{3}}=\frac{3}{2}M{{R}^{2}}\]                 So,          \[{{I}_{YY'}}=\frac{1}{2}M{{R}^{2}}+\int_{{}}^{{}}{\left( \frac{3}{2}M{{R}^{2}}+\frac{3}{2}M{{R}^{2}} \right)}=\frac{7}{2}M{{R}^{2}}\]


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