A satellite of mass $m$ revolves around the earth of radius $R$ at a height $x$ from its surface. If $g$ is…

A satellite of mass $m$ revolves around the earth of radius $R$ at a height $x$ from its surface. If $g$ is the acceleration due to gravity on the surface of the earth, the orbital speed of the satellite is
  1. $g x$
  2. $\frac{\mathrm{gR}}{\mathrm{R}-\mathrm{x}}$
  3. $\frac{g^2}{R+x}$
  4. $\left(\frac{g R^2}{R+x}\right)^{1 / 2}$

Solution

For the satellite, the gravitational force provides the necessary centripetal force i.e. $ \begin{aligned} & \frac{\mathrm{GM}_{\mathrm{e}} \mathrm{m}}{(\mathrm{R}+\mathrm{X})^2}=\frac{\mathrm{Mv}_0^2}{(\mathrm{R}+\mathrm{X})} \text { and } \frac{\mathrm{GM}_{\mathrm{e}}}{\mathrm{R}^2}=\mathrm{g} \\ & \therefore \mathrm{v}_0=\left(\frac{g \mathrm{R}^2}{\mathrm{R}+\mathrm{X}}\right)^{1 / 2} \\ & \end{aligned} $

Asked in: JEE Main 2004

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