AFMC AFMC Solved Paper-2010

  • question_answer
    The ratio of the radii of gyration of a circular disc and a circular ring of the same radii about a tangential axis perpendicular to plane of disc or ring is

    A) 1 : 2                                       

    B) \[\sqrt{5}\,:\,\sqrt{6}\]

    C) 2 : 3                                       

    D) \[\frac{\sqrt{3}}{2}\]

    Correct Answer: D

    Solution :

    Radius of gyration\[K=\sqrt{\frac{I}{m}}\] (where J is moment of inertia) \[{{K}_{disc}}=\sqrt{\frac{\frac{1}{2}m{{R}^{2}}+m{{R}^{2}}}{m}}=\sqrt{\frac{3}{2}}R\] \[{{K}_{ring}}=\sqrt{\frac{m{{R}^{2}}+m{{R}^{2}}}{m}}=\sqrt{2}R\] \[\therefore \]  \[\frac{{{K}_{disc}}}{{{K}_{ring}}}=\frac{\sqrt{\frac{3}{2}}}{\sqrt{2}}=\frac{\sqrt{3}}{2}\]


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