The height ' $h$ ' above the earth's surface at which the value of acceleration due to gravity ( g ) becomes…

The height ' $h$ ' above the earth's surface at which the value of acceleration due to gravity ( g ) becomes $\left(\frac{\mathrm{g}}{3}\right)$ is ( $\mathrm{R}=$ radius of the earth)
  1. $\quad(\sqrt{3}+1) \mathrm{R}$
  2. $(\sqrt{3}-1) R$
  3. $\sqrt{3} R$
  4. $3 \sqrt{R}$

Solution

We know that, $\begin{aligned} & \mathrm{g}_{\mathrm{h}}=\mathrm{g}\left(\frac{\mathrm{R}}{\mathrm{R}+\mathrm{h}}\right)^2 \\ & \text { For } g_h=\frac{g}{3} \\ & \frac{g}{3}=g\left(\frac{R}{R+h}\right)^2 \\ & \frac{1}{\sqrt{3}}=\frac{\mathrm{R}}{\mathrm{R}+\mathrm{h}} \\ & \sqrt{3} \mathrm{R}=\mathrm{R}+\mathrm{h} \\ & \therefore \quad h=(\sqrt{3}-1) \mathrm{R} \end{aligned}$

Asked in: MHT CET 2024 (04 May Shift 1)

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