J & K CET Engineering J and K - CET Engineering Solved Paper-2006

  • question_answer
    If the angular momentum of a rotating body about a fixed axis is increased by\[10%\]. Its kinetic energy will be increased by

    A)  \[10%\]        

    B)  \[20%\]

    C)  \[21%\]        

    D)  \[5%\]

    Correct Answer: C

    Solution :

    Kinetic Energy \[K=\frac{{{J}^{2}}}{2I}\] where J is angular momentum and \[I\] the moment of inertia. \[\therefore \] \[{{K}_{1}}=\frac{{{J}^{2}}}{2I},\,\,\,\,\,{{K}_{2}}=\frac{{{\left( J+\frac{10}{100}J \right)}^{2}}}{2I}\] \[\therefore \] \[\frac{{{K}_{1}}}{{{K}_{2}}}=\frac{{{(100)}^{2}}}{{{(110)}^{2}}}=\frac{100}{121}\] % change \[=\frac{{{K}_{2}}-{{K}_{1}}}{{{K}_{1}}}=\frac{{{K}_{2}}}{{{K}_{1}}}-1\] \[=\frac{121}{100}-1=21%\]


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