CMC Medical CMC-Medical VELLORE Solved Paper-2011

  • question_answer
    The change in potential energy when a body of mass m is raised to a height nR from the centre of earth (R = radius of earth)

    A)  \[mgR\frac{\left( n-1 \right)}{n}\]                          

    B)  \[nmgR\]

    C)  \[mgR\left( \frac{{{n}^{2}}}{{{n}^{2}}+1} \right)\]           

    D)  \[mgR\left( \frac{n}{n+1} \right)\]

    E)  mgR

    Correct Answer: A

    Solution :

                    The  change  in  potential  energy gravitational field is given by \[\Delta E=GMm\left( \frac{1}{{{r}_{1}}}-\frac{1}{{{r}_{2}}} \right)\] In this problem, \[{{r}_{1}}=R\] and \[{{r}_{2}}=nR\] \[\Delta E=GMm\left( \frac{1}{R}-\frac{1}{nR} \right)\] \[=\frac{GMm}{R}\left( \frac{n-1}{n} \right)\] \[=mgR\left( \frac{n-1}{n} \right)\]          \[\left[ \because g=\frac{GM}{{{R}^{2}}} \right]\]


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