CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2007

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

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

    B)  \[mgR\]              

    C)         \[mgR=\frac{n}{(n+1)}\]

    D)         \[mgR=\frac{{{n}^{2}}}{({{n}^{2}}+1)}\]

    E)  \[\frac{mgR}{n}\]

    Correct Answer: C

    Solution :

    Change in potential energy \[\Delta U={{U}_{2}}-{{U}_{1}}\] \[\therefore \]  \[\Delta U=-\frac{GMm}{(R+nR)}+\frac{GMm}{R}\] Or           \[\Delta U=-\frac{GMm}{R(1+n)}+\frac{GMm}{R}\] Or           \[\Delta U=\frac{GMm}{R}\left[ -\frac{1}{1+n}+1 \right]\] Or           \[\Delta U=\frac{({{R}^{2}}g)m}{R}\times \frac{n}{(1+n)}\]\[\left[ \because g=\frac{GM}{{{R}^{2}}} \right]\] Or           \[\Delta U=mgR\left( \frac{n}{n+1} \right)\]


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