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JCECE Engineering JCECE Engineering Solved Paper-2008

  • question_answer
    The mass of the earth is \[6.00\times {{10}^{24}}kg\] and that of the moon is\[7.40\times {{10}^{22}}kg\]. The constant of gravitation\[G=6.67\times {{10}^{-11}}N\text{-}{{m}^{2}}/k{{g}^{2}}\]. The potential energy of the   system   is\[-7.79\times {{10}^{28}}J\]. The mean distance between the earth and moon is

    A) \[3.80\times {{10}^{8}}m\]                         

    B) \[3.37\times {{10}^{6}}m\]

    C)  \[7.60\times {{10}^{4}}m\]                        

    D)  \[1.90\times {{10}^{2}}m\]

    Correct Answer: A

    Solution :

    \[U=\frac{GMm}{r}\] \[\Rightarrow \]               \[7.79\times {{10}^{28}}\]                 \[=\frac{6.67\times {{10}^{-11}}\times 7.4\times {{10}^{22}}\times 6\times {{10}^{24}}}{r}\] \[\Rightarrow \]               \[r=3.8\times {{10}^{8}}m\]


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