BCECE Engineering BCECE Engineering Solved Paper-2008

  • question_answer
    If distance between earth and sun become 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 and R is semi-major 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 be T. \[\therefore \]  \[{{T}^{2}}=k{{(4R)}^{3}}\]                           ?(i) \[\therefore \]  \[\frac{{{T}^{2}}}{T{{}^{2}}}=\frac{1}{64}\] or            \[\frac{T}{T}=\frac{1}{8}\] or            \[T=8T\] So, time period becomes 8 times of previous value.


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