Calculating Graviational Field

[areed6]

Homework Statement

Calculate the gravitational field associated with a 1015 kg mass, at a distance 20 km (r) from the center of that mass. Express your answer in both ‘Gravity Units’ and “Gals”. Assume that the radius of the mass is much less than 30 km, and that the mass can therefore be treated as a point source.

Homework Equations

The mean value of gravity at the earth’s surface is about 9.80 m/s2.
Basic gravitational equation:
g = GM/R2
G - gravitational constant M - mass of the Earth R - radius of Earth

9.8 m/s2 = 980 Gal
1 mGal = 0.001 Gal
1 μGal = 0.001mGal = 10-6 Gal
1 gu (gravity unit) = 0.1 mGal = 10-4 Gal

The Attempt at a Solution

I'm a graduate student with a degree in criminal justice... We couldn't come up with any coherent answers.

[(9.8m/s^2)*(10^15kg)]/20km^2

4.9*10^8kg m/s2

 

[nasu]

The G in the formula is not 9.8 m/s^2. Look up universal gravitational constant.
And you need your units to be coherent.