Sol. $$ \mathrm{M}=\frac{\mathrm{W}}{\mathrm{~g}}=\frac{200}{10}=20 \mathrm{~kg} $$ Acc. Due to gravity at a depth $\mathrm{g}^{\prime}=\mathrm{g}\left(1-\frac{\mathrm{d}}{\mathrm{R}}\right)$ $$ \begin{aligned} & d \rightarrow \text { depth from surface } \\ & d=\frac{R}{2} \\ & g^{\prime}=g\left(1-\frac{R / 2}{R}\right)=\frac{g}{2}=5 \mathrm{~m} / \mathrm{s}^2 \\ & \text { weight }=m \times g \\ & \text { at depth } R / 2=20 \times 5=100 \mathrm{~N} \end{aligned} $$