Explanation:
Acceleration due to gravity at a depth \(d\) from surface of earth
\({g^\prime } = g\left( {1 - \frac{d}{R}} \right){\mkern 1mu} {\mkern 1mu} \,\,\,\,\,\,\,\,\,\,(1)\)
Where \(g=\) acceleration due to gravity at earth's surface
Multiplying by mass ' \(m\) ' on both sides of (1)
\(\begin{aligned}& m g^{\prime}=m g\left(1-\dfrac{d}{R}\right) \quad\left(d=\dfrac{R}{2}\right) \\& =200\left(1-\dfrac{R}{2 R}\right)=\dfrac{200}{2}=100 N\end{aligned}\)