J & K CET Engineering J and K - CET Engineering Solved Paper-2012

  • question_answer
    Taking the radius of the earth to be \[6400\text{ }km,\] by what percentage will the acceleration due to gravity at a height of \[100\text{ }km\]from the surface of the earth differ from that on the surface of the earth?

    A)  About 1.5%     

    B)  About 5%

    C)  About 8%       

    D)  About 3%

    Correct Answer: D

    Solution :

    Here, \[{{R}_{e}}=600km\] \[h=100\,km\] Acceleration due to gravity at height, h \[g'=\frac{gR_{e}^{2}}{{{({{R}_{e}}+h)}^{2}}}\] \[g'=\frac{g{{(6400)}^{2}}}{{{(6400+100)}^{2}}}\] \[=g{{\left( \frac{6400}{6500} \right)}^{2}}\] Percentage change in acceleration due to gravity \[=\frac{g-g'}{g}\times 100%\] \[=\left( 1-\frac{g'}{g} \right)\times 100%\] \[={{\left[ 1-\frac{6400}{6500} \right]}^{2}}\times 100%\] \[=3.05%\]


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