Help PLEASE! Gravitational Strength

[Jtappan]

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

(a) Find the altitude above the Earth's surface where Earth's gravitational field strength would be two-thirds of its value at the surface. Assume re = 6.371 103 km.
km
(b) Find the altitude above the Earth's surface where Earth's gravitational field strength would be one-third of its value at the surface.
km



2. Relevant equations

m = (GMe/Re^2)

3. The attempt at a solution

Im not entirely sure the equation is right for this type of problem. I do not even know where to start for this problem.

[Saladsamurai]

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

(a) Find the altitude above the Earth's surface where Earth's gravitational field strength would be two-thirds of its value at the surface. Assume re = 6.371 103 km.
km
(b) Find the altitude above the Earth's surface where Earth's gravitational field strength would be one-third of its value at the surface.
km



2. Relevant equations

m = (GMe/Re^2)

3. The attempt at a solution

Im not entirely sure the equation is right for this type of problem. I do not even know where to start for this problem.


I think your equation is wrong. F_g=\frac{GMm}{r^2}

Do you know how to set up a proportion of equations?

[Jtappan]

Could you please explain how to do that? :-)