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JEE Main & Advanced JEE Main Paper (Held On 11-Jan-2019 Evening)

  • question_answer
    A circular disc \[{{D}_{1}}\] of mass M and radius R has two identical discs \[{{D}_{2}}\] and \[{{D}_{3}}\]of the same mass M and radius R attached rigidly at its opposite ends (see figure). The moment of inertia of the system about the axis OO?, passing through the centre of \[{{D}_{1}}\], as shown in the figure, will be [JEE  Main Online Paper (Held on 11-jan-2019 Evening)]

    A) \[3M{{R}^{2}}\]                                 

    B) \[\frac{4}{5}M{{R}^{2}}\]

    C) \[\frac{2}{3}M{{R}^{2}}\]                  

    D)   \[M{{R}^{2}}\]

    Correct Answer: A

    Solution :

    \[I={{I}_{1}}+{{I}_{2}}+{{I}_{3}}={{I}_{1}}+2\times {{I}_{2}}\]   \[(\because {{I}_{2}}={{I}_{3}})\] \[=\frac{1}{2}M{{R}^{2}}+2\times (M{{R}^{2}}+\frac{M{{R}^{2}}}{4})=3M{{R}^{2}}\]


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