Manipal Medical Manipal Medical Solved Paper-2005

  • question_answer
    The ratio of radii of gyration of a circular disc and a circular ring of the same radii and same mass about a tangential axis in the plane is:

    A)  \[1:2\]

    B)  \[\sqrt{5}:\sqrt{6}\]

    C)  \[2:3\]

    D)  \[2:1\]

    Correct Answer: B

    Solution :

     \[{{I}_{ring}}=\frac{m{{r}^{2}}}{2}+m{{r}^{2}}=\frac{3}{2}m{{r}^{2}}\] \[{{I}_{disc}}=\frac{m{{r}^{2}}}{2}+m{{r}^{2}}=\frac{5}{4}m{{r}^{2}}\] \[\frac{{{I}_{disc}}}{{{I}_{ring}}}=\frac{\frac{5m{{r}^{2}}}{4}}{\frac{3}{2}m{{r}^{2}}}=\frac{5}{6}\] \[\frac{m{{k}^{2}}_{disc}}{m{{k}^{2}}_{ring}}=\frac{5}{6}\] \[\Rightarrow \] \[\frac{{{k}_{disc}}}{{{k}_{ring}}}=\sqrt{\frac{5}{6}}\] \[=\sqrt{5}:\sqrt{6}\]


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