Calculating Weight in Orbit: How Does Distance Affect Gravitational Force?

[abpandanguyen]

Homework Statement

A mass weighs 20 N at the surface of a planet of 3000 km radius. What is the mass's weight when it is in orbit 3000 km above the surface of the planet?

Homework Equations

F = (Gm₁m₂)/r² (well... not really)
U_g = mgy

The Attempt at a Solution

I don't even know. I'm trying to find the g on this planet but I'm not sure where that would lead me... Help please >_<

 

[rock.freak667]

what is the new 'r' you want to find? How does that relate to the original 'r'?

r= r at surface then

GMm/r²= ?

 

[abpandanguyen]

yeah, i just needed to write the equations out instead of just thinking in my head

thanks!