A uniform sphere of mass 64kg and radius 4m , a concentric cavity of radius 1m is made. The gravitational force on a mass of 1kg  at a distance of 2m from the center of the spheres is (take $G=6.67\times {10}^{-11}N{m}^2/k{g}^2$ )

$E_{net}=$Field at an interior point of solid sphere. Field at an exterior point of cavity.

$\begin{array}{l}mass of given sphere=M=64\mathrm{kg}; mass of cavity=M^1; univform density=\rho \\ \frac{M^1}{M}=\frac{\frac{4}{3}\pi 1^3\times \rho }{\frac{4}{3}\pi 4^3\times \rho }\\ M^1=\frac{M}{64}=1\mathrm{kg}=mass of cavity---\left(1\right)\end{array}$

$\begin{array}{l}gravitational field strength=E_{\text{net }}=E_{\text{solid }}\text{ sphere interior point }-E_{\text{cavity }}\\ E_{\text{solid }}=\frac{GMr}{R^3}\\ E_{\text{cavity }}=\frac{G{M}^1}{r^2}\\ E_{\text{net }}=\frac{G\left(64\right)2}{4^3}-\frac{G\times \left(1\right)}{2^2}\\ E_{\text{net }}=2G-\frac{G}{4}=\frac{7G}{4}\\ E_{\text{net }}=11.67\times {10}^{-11}\mathrm{N}/\mathrm{kg}\\ E_{net}=11.7\times {10}^{-11}N/\mathrm{kg}\\ \therefore \text{ Gravitational force is }F=m\times E_{net}=1\times 11.7\times {10}^{-11}=11.7\times {10}^{-11}N\end{array}$