Change in Magnitude of Accleration due to gravity

[mandi182]

Homework Statement

When searching for gold, measurements of g can be used find regions within the Earth where the density is larger than that of normal soil. Such measurements can also be used to find regions in which the density of the Earth is smaller than normal soil; such regions might contain a valuable fluid (oil). Consider a deposit of oil that is 350 m in diameter and just below the surface of the Earth. For simplicity, assume the deposit is spherical. Estimate the change in the magnitude of the acceleration due to gravity on the surface above this deposit. Assume that the density of the oil is 1590 kg/m3 and the density of normal soil and rock is 2500 kg/m3. Note: Companies that search for valuable minerals actually use this method.

Homework Equations

a=GM/r^2 and also 4/3pi (r^3)

The Attempt at a Solution

I solved for the Mass of each which was 3.57E10 and 5.612E10. Then I solved for accelaration due to gravity on both, which was 1.2228168630857E-5 and 7.777E-6
and then subtracted those numbers to get the change in acceleration due to gravity.

The answer I got was incorrect, so I am not sure what to do next.

Thanks!

 

[Delphi51]

I get the same numbers for the masses, but not for the accelerations.
Try that last calc again and show your work if you would like more feedback.