Question

The center of a 1.10km diameter spherical pocket of oil is 1.10km beneath the Earth's surface.

Estimate by what percentage directly above the pocket of oil would differ from the expected value of for a uniform Earth? Assume the density of oil is .
Express your answer using two significant figures.

Answer 1

Subtract from the "normal" value of g the acceleration in the opposite direction due to a hypothetical sphere of negative mass equal to the difference between the mass of earth's crust and the same volume full of oil. This reduction in g will be equal to
a = G (Mcrust-Moil)/(0.55*10^3 m)^2
Insert the appropriate M values for a sphere of earth's crust and a sphere of oil.