Haryana PMT Haryana PMT Solved Paper-2007

  • question_answer
    If distance between earth and sun becomes four times, then time period becomes

    A)  4 times                               

    B)  8 times

    C)  1/4 times                           

    D)  1/8 times

    Correct Answer: B

    Solution :

                    Key Idea Keplers third law is applicable here. According to Keplers third law (law of periods), the square of the time period of revolution of a planet around the sun is directly proportional to the cube of semi major axis of its elliptical orbit,        ie,           \[{{T}^{2}}\propto {{R}^{3}}\] where T is time taken by the planet to go once around the sun. R is semimajor axis (distance) of the elliptical orbit. \[\therefore \]  \[{{T}^{2}}=k{{R}^{3}}\]              ???.(i)  (where k is constant of proportionality) When R becomes 4 times, let; time period become T. \[\therefore \]  \[{{T}^{2}}=k{{(4R)}^{3}}\]          ??.(ii) \[\therefore \]  \[\frac{{{T}^{2}}}{T{{}^{2}}}=\frac{1}{64}\] or            \[\frac{T}{T}=\frac{1}{8}\] or            \[T=8T\] So, time period becomes 8 times of previous value.             


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