Homework Help: Universal Gravitation Question (solving for distance)

1. Dec 18, 2011

lindsey0307

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

A space vehicle of mass 555kg, experiences a gravitational pull from Earth of 255N. The mass of Earth is 5.98x10 (to the power of 24) kg.How far is the vehicle a) from the center of the Earth, and b) above the surface of the Earth?

2. Relevant equations
FG = GM1M2/d squared

3. The attempt at a solution
I rearranged the equation above, and solved for d (the radius) and got the answer 2.95x10(to the power of 7) m, which I believe is correct. However, I can't seem to figure out how to find part b) or even what variable I am solving for. I'm not solving for the radius because I already did that in a) so I think I'll have to alter the equation somehow. Any help would be greatly appreciated!

2. Dec 18, 2011

Staff: Mentor

d stands for the distance of the object from the center of the earth, not the radius of anything.
Hint: What's the radius of the earth? (Look it up.)

3. Dec 18, 2011

technician

I got the same answer as you for the radius (distance from the centre of the Earth)
To find the height above the surface of the Earth you need to know the radius of the Earth.... do you have that?

4. Dec 18, 2011

lindsey0307

Oh, I just realized I do have the radius of Earth on my formula sheet (which we've never needed to use before). It says it is 6.28x10 (to the power of 6) m.

5. Dec 18, 2011

lindsey0307

Now I've got the answer! I just subtracted the radius of earth from my answer in a). Ah, i should've realized that...thank you!