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 15.0 X 103 kg/m3 at the center and 2.0 X 103 kg/m3 at the surface. What is the acceleration due to gravity at the surface of this planet?