Manipal Engineering Manipal Engineering Solved Paper-2008

  • question_answer
    The period of a planet around sun is 27 times that of earth. The ratio of radius of planets orbit to the radius of earths orbit is

    A)  4            

    B)         9

    C)  64                         

    D)         27

    Correct Answer: B

    Solution :

    From Keplers third law of planetary motion. The square of the period of revolution\[(T)\]of any planet around the sun is directly proportional to the cube of the semi major axis\[(X)\]of its elliptical orbit \[ie,\]    \[{{T}^{2}}\propto {{R}^{3}}\] Given,   \[{{T}_{p}}=27{{T}_{e}},\]                 \[\frac{T_{e}^{2}}{T_{p}^{2}}=\frac{R_{e}^{3}}{R_{p}^{3}}\]                 \[\frac{T_{e}^{2}}{{{(27{{T}_{e}})}^{2}}}=\frac{R_{e}^{3}}{R_{p}^{3}}\]                 \[\frac{{{R}_{p}}}{{{R}_{e}}}={{(27)}^{2/3}}\]                 \[\frac{{{R}_{p}}}{{{R}_{e}}}={{3}^{2}}\]                 \[{{R}_{p}}=9{{R}_{e}}\]


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