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.

Visualize the problem and identify special cases first examine the problem by drawing a picture and visualizing the motion. apply newton's 2nd law, ∑f⃗ =ma⃗ , to each body in your mind. don't worry about which quantities are given. think about the forces on each body: how are these consistent with the direction of the acceleration for that body? can you think of any special cases that you can solve quickly now and use to test your understanding later? one special case in this problem is if m2=0, in which case block 1 would simply fall freely under the acceleration of gravity: a⃗ 1=−gj^.