Force Of gravity

[mr.mair]

1. The problem statement, all variables and given/known data

If the earth radius is 6.4 X 10^3 km, calculate the force of gravity on a 1.0 X 10^5 kg space station situated
(a) earth surface
(b) 1.28 X 10^5 km from the center of the earth
(c) 3.84 X 10^5 from the center of the earth ( about the distance to the moon)
(d) 1.5 X 10^8 km from the center of the earth ( about the distance of the sun)

2. Relevant equations
Fg = mg


3. The attempt at a solution

Question a

Fg= (100000)(9.8)
Fg= 980000

questions b - d have been attemped but have no idea on these plz help

[GRB 080319B]

Fg = mg only applies to objects less than 100 km from the Earth's surface. For b.,c., and d. you must use Fg = Gm1m2/r^2, where G is the gravitational constant, m1 and m2 are masses of Earth and satellite respectively, and r is the distance from the center of Earth to satellite.