Question
State the formula for acceleration due to gravity at depth ' $d$ ' and altitude ' $h$ ' Hence show that their ratio is equal to $\left(\frac{R-d}{R-2 h}\right)$ by assuming that the altitude is very small as compared to the radius of the Earth.

Answer

For an object at depth d, acceleration due to gravity of the Earth is given by,
$
g_d=g\left(1-\frac{ d }{ R }\right)
$
2. Also, the acceleration due to gravity at smaller altitude $h$ is given by,
$
g _{ h }= g \left(1-\frac{2 h }{ R }\right)
$
3. Hence, dividing equation (1) by equation (2),
we get,
$
\begin{aligned}
\frac{g_d}{g_h} & =\frac{g\left(1-\frac{d}{R}\right)}{g\left(1-\frac{2 h}{R}\right)}=\frac{R-d}{R} \times \frac{R}{R-2 h} \\
\therefore \quad \frac{g_d}{g_h} & =\frac{R-d}{R-2 h}
\end{aligned}
$

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