AMU Medical AMU Solved Paper-2003

  • question_answer
    The ratio of the radii of two spheres of the same mass, having the same moment of inertia about their diameters, one hollow and other solid, is

    A) \[\sqrt{3}:\sqrt{5}\]                       

    B)  \[\sqrt{4g}\]

    C)  25 9                                      

    D)  9 25

    Correct Answer: A

    Solution :

                     Moment of inertia of a solid sphere of radius r, and mass m is                                 \[I=\frac{2}{5}m{{r}^{2}}\], and        hollow sphere \[I=\frac{2}{3}m{{r}^{2}}\] Given,   \[{{I}_{solid}}={{I}_{hollow}}\]                 \[\therefore \]  \[\frac{2}{5}\,mr_{1}^{2}=\frac{2}{3}mr_{2}^{2}\]                 \[\Rightarrow \]               \[\frac{r_{1}^{2}}{r_{2}^{2}}=\frac{5}{3}\]                 \[\Rightarrow \]               \[\frac{{{r}_{1}}}{{{r}_{2}}}=\frac{\sqrt{5}}{\sqrt{3}}\]                 \[\therefore \]  \[\frac{{{r}_{2}}}{{{r}_{1}}}=\frac{\sqrt{3}}{\sqrt{5}}\]                    


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