AMU Medical AMU Solved Paper-2011

  • question_answer
    A small planet is revolving around a very massive star in a circular orbit of radius R with a period of revolution T. If the gravitational force between the planet and the star were proportional to \[{{R}^{-5/2}},\] then T would be proportional to

    A) \[{{R}^{3/2}}\]                                  

    B)  \[{{R}^{3/5}}\]

    C)  \[{{R}^{7/2}}\]                                 

    D)  \[{{R}^{7/4}}\]

    Correct Answer: D

    Solution :

                     For revolution of planet centripetal force is provided by gravitational force of attraction                 \[m{{\omega }^{2}}R\propto {{R}^{-5/2}}\]                                 \[\frac{1}{{{T}^{2}}}\propto {{R}^{-7/2}}\]            \[\left[ \because \omega =\frac{2\pi }{T} \right]\]                 or            \[{{T}^{2}}\propto {{R}^{7/2}}\]                 or            \[T\propto {{R}^{7/4}}\]


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