JEE Main & Advanced Sample Paper JEE Main Sample Paper-40

  • question_answer
    Suppose the gravitational force varies inversely as the nth power of the distance. Then the time period of a planet in circular orbit of radius R around the sun will be proportional to

    A) \[{{R}^{n}}\]                                  

    B) \[{{R}^{-n}}\]

    C) \[{{R}^{(n+1)2}}\]             

    D) \[{{R}^{(n-1)/2}}\]

    Correct Answer: C

    Solution :

    \[T=\frac{2\pi R}{v}\]??.(1); \[V={{\left[ \frac{2GM}{{{R}^{n-1}}} \right]}^{1/2}}\]?.(2) \[E=\frac{1}{2}m{{v}^{2}}=\frac{GMm}{{{R}^{n-1}}}\] From (1) & (2), \[T=-\frac{2\pi R}{\sqrt{\frac{2GM}{{{R}^{n-1}}}}}=\frac{2\pi R}{\sqrt{\frac{2GM}{{{R}^{n-1}}}}}=\frac{2\pi }{\sqrt{2GM}}\times {{R}^{(n+1)/2}}.\] Therefore, \[T\propto {{R}^{(n+1)/2}}\]


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