NTSE Sample Paper NTSE SAT Practice Test-9

  • question_answer
    If a planet existed whose mass and radius were both half those of the earth, the acceleration due to gravity at its surface would be

    A) \[19.6\,m{{s}^{-2}}\] 

    B) \[9.8\,m{{s}^{-2}}\]

    C) 4.9 \[m{{s}^{-2}}\]                 

    D) 2.45 \[m{{s}^{-2}}\]

    Correct Answer: A

    Solution :

    [a] Acceleration due to gravity (g?) on the planet is given by, g' = \[\frac{GM}{{{R}^{2}}}\], where M is mass and R is radius of the planet. We have, \[M=\frac{{{M}_{e}}}{2}\] and \[R=\frac{{{R}_{e}}}{2}\] \[\therefore g'=\frac{\frac{G{{M}_{e}}}{2}}{{{\left( \frac{{{R}_{e}}}{2} \right)}^{2}}}=\frac{2G{{M}_{e}}}{{{R}_{e}}^{2}}=2{{g}_{e}}\] \[=2\times 9.8=19.6\,\,\,m{{s}^{-2}}\] 


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