Planets are not uniform inside. normally, they are densest at the center and have decreasing density outward toward the surface. model a spherically symmetric planet, with the same radius as the earth, as having a density that decreases linearly with distance from the center. let the density be 1.60×10⁴ kg/m³ at the center and 2400 kg/m³ at the surface. g= 6.67×10⁻¹¹ n*m²/kg², and the radius of the earth to be r= 6.38×10⁶ m.