1. The problem statement, all variables and given/known data There is a planet (spherical) with a hollow that is concentric with the planet.if the inner radius is r and outer radius is R and mass of the planet is M what would the gravity be outside of the planet at distance x from the center ? 2. Relevant equations Shell theorem Universal law of gravity 3. The attempt at a solution I am confused about whether you can treat hollow sphere as if the mass is concentrated in the middle or if you have to subtract the gravity of the large sphere with gravity of the cavity. So , is it correct to say that the gravity at distance x is actually gravity of a planet with radius R minus gravity of planet with radius r ?