BCECE Medical BCECE Medical Solved Papers-2015

  • question_answer
    A solid cylinder of mass 20 kg rotates about its axis with angular speed 100 rad \[{{s}^{-1}}\]. The radius of the cylinder is 0.25 m. What is the kinetic energy associated with the rotation of cylinder? What is the magnitude of angular momentum of cylinder about its axis?

    A)  62.5 T-s

    B)  70.4 T-s

    C)  79.6 T-s

    D)  60.5 T-s

    Correct Answer: A

    Solution :

    If I be the moment of inertia of the cylinder about its axis, then \[I=\frac{1}{2}M{{R}^{2}}=\frac{1}{2}\times 20\times {{(0.25)}^{2}}=0.625\,kg-{{m}^{2}}\] \[\therefore \,KE\] associated with the rotating cylinder is given by,         \[KE=\frac{1}{2}I{{\omega }^{2}}=\frac{1}{2}\times 0.625\times {{(100)}^{2}}=3125\,J\] Also using the relation,                 \[L=\sqrt{2I\,(KE)}\] We have \[L=\sqrt{2\times 0.625\times 3125}\] \[L=62.5\,J-s\]


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