일반물리학 1 — Gravitation: Problem 13

13 One model for a certain planet has a core of radius R and mass M surrounded by an outer shell of inner radius R, outer radius 2R, and mass 4M. If M = 3.00 x 10^24 kg and R = 12 x 10^6 m, what is the gravitational acceleration of a particle at points (a) R and (b) 3R from the center of the planet?