Gravitational Force on 0.64 kg Sphere in Space Shuttle

[nweis84]

I have this problem i have been trying to solve and can't seem to get it right. The question states:

The space shuttle is in orbit 396.9 km above the surface of the earth. What is the gravitational force on a 0.64 kg sphere inside the space shuttle?

mass Earth = 5.98x10^24 kg
radius of Earth = 6.37x10^6 m

I've tried using the equation F= (G*M*m)/r^2 and the answer i got was about 5.57 N

for the distance above Earth i converted the units and added them to the Earth's radius so I'm not sure what I could be doing wrong.

is it possible that i am using the wrong equation all together?

 

[carrotcake10]

r is defined as being the distance between the two point masses.

I might be wrong, but for this problem, would you not just use the distance from Earth as r?

 

[tnutty]

F = GMm/r^2 , G is the universal gravity, M is mass of the object acting the force,
m is the mass of the object that the force is acted upon, r is the distance between the center of the Earth and the center of the object in space.