JEE Main & Advanced JEE Main Paper (Held On 09-Jan-2019 Evening)

  • question_answer
    The energy required to take a satellite to a height 'h' above Earth surface (radius of Earth \[=6.4\times {{10}^{3}}km\]) is \[{{E}_{1}}\] and kinetic energy required for the satellite to be in a circular orbit at this height is \[{{E}_{2}}\]. The value of h for which \[{{E}_{1}}\] and \[{{E}_{2}}\] are equal, is: [JEE Main Online Paper (Held On 09-Jan-2019 Evening]

    A) \[3.2\times {{10}^{3}}\text{ }km\]

    B) \[1.6\times {{10}^{3}}km\]

    C) \[1.28\times {{10}^{4}}km\]

    D) \[6.4\times {{10}^{3}}km\]

    Correct Answer: A

    Solution :

    \[{{E}_{2}}\,=\,\frac{GMm}{2(R+h)}\] \[{{E}_{1}}\,=\,\frac{GMm}{R}\,-\,\frac{GMm}{(R+h)}\] \[\,\frac{GMm}{2(R+h)}\,=\,GMm\,\left[ \frac{1}{R}-\frac{1}{R+h} \right]\] \[\frac{1}{2(R+h)}\,\,=\,\left[ \frac{R+h-R}{R(R+h)} \right]\] \[h=\frac{R}{2}\,=\,\frac{6.4\,\times \,{{10}^{3}}}{2}\,\,=\,\,3.2\,\times \,{{10}^{3}}\,km\]                 


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