The density inside a solid sphere of radius a is given by ρ = ρ0 (a/r), where ρ0 is the density at the surface and r denotes the distance from the centre. The gravitational field due to this sphere at a distance 3a from its centre is
1
\(\frac{2}{3} \pi \rho_0 a\)
2
\(\frac{4 \pi}{3} \mathrm{G} \rho_0 a^2\)
3
\(\frac{2}{9} \pi \mathrm{G} \rho_0 a\)
4
\(\frac{4 \pi \mathrm{G} \rho_0}{9 a^2}\)