RAJASTHAN ­ PET Rajasthan PET Solved Paper-2011

  • question_answer
    On a massless rod four masses are fixed as shown in figure. What is the moment of inertia about an axis passing through centre of rod

    A)  \[\frac{{{l}^{2}}}{2}\left( M+\frac{m}{4} \right)\]

    B)  \[\frac{{{l}^{2}}}{2}\left( \frac{M}{4}+m \right)\]

    C)  \[\frac{{{l}^{2}}}{4}\left[ M+\frac{m}{4} \right]\]

    D)  \[\frac{{{l}^{2}}}{4}\left[ \frac{M}{4}+m \right]\]

    Correct Answer: A

    Solution :

     Moment of inertia of mass M about axis \[=M\times {{\left( \frac{l}{2} \right)}^{2}}\] Moment of inertia of both the masses having mass\[M=2M\times {{\left( \frac{l}{2} \right)}^{2}}=\frac{M{{l}^{2}}}{2}\] Moment of inertia of masses having mass \[m=2\times m{{\left( \frac{l}{4} \right)}^{2}}=\frac{m{{l}^{2}}}{8}\] Therefore, total moment of inertia \[=\frac{M{{l}^{2}}}{2}+\frac{m{{l}^{2}}}{8}\] \[=\frac{{{l}^{2}}}{2}\left[ M+\frac{m}{4} \right]\]


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