AFMC AFMC Solved Paper-2009

  • question_answer
    A thin circular ring of mass M and radius R is rotating about its axis with a constant angular velocity\[\omega \]. Two objects, each of mass m, are connected gently to the ring. The ring now rotates with an angular velocity

    A) \[\frac{\omega M}{M+m}\]

    B) \[\frac{\omega \left( M-2M \right)}{\left( M+2m \right)}\]

    C) \[\frac{\omega \left( M+2m \right)}{M}\]                           

    D) \[\frac{\omega M}{M+2m}\]

    Correct Answer: D

    Solution :

    Initial angular momentum of ring\[L=I\omega =M{{R}^{2}}\omega \]Final angular momentum of ring and two particle system \[L=(M{{R}^{2}}+2m{{R}^{2}})\omega '\]                 As there is no torque on the system, therefore angular momentum remains constant, \[\ \therefore \]  \[M{{R}^{2}}\omega =(M{{R}^{2}}+2m{{R}^{2}})\omega '\]\[\Rightarrow \]   \[\omega '=\frac{M\omega }{M+2m}\]


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