Question 1 requires short answers 2 and 3 are general answers. Thanks

gbi DEEEE2 253st When we think about gravity, we typically think about two different domains. One is on the surface of the Earth, where g=9.8m/s2. The other is above the surface, where gravity drops off as 1/r2 (remembering that r is measured from the center of the planet, not the surface). But there's a third region we can think about, underground. When we look at the formula for gravity, E=e GMm/rZ, where M is the mass of one of the bodies. As you tunnel into the Earth, the effective mass involved in this equation drops. Newton, through some involved proofs, showed that the formula for the effective M should be the density of the Earth multiplied by the volume of a sphere with radius r (note that this is true for r