# Finding Altitude

1. Aug 30, 2009

### slu1986

1. (a) Find the altitude above the Earth's surface where Earth's gravitational field strength would be four-fifths of its value at the surface. Assume re = 6.371*10^3 km.

(b) Find the altitude above the Earth's surface where Earth's gravitational field strength would be one-fifth of its value at the surface.

2. Relevant equations
g= GMe/re^2
G= 6.67*10^-11 Nm^2/kg^2
Me= 5.98*10^24 kg

3. I am so lost when I try to solve this problem. Could someone please guide me in the right direction to solving this problem. I would greatly appreciate it.

2. Sep 1, 2009

### tiny-tim

Hi slu1986!

(try using the X2 and X2 tags just above the Reply box )

This is a dimensions question …

(like, if the radius is multiplied by three, how much is the surface area multiplied by?)

so ask yourself, on what power of r does the gravitational field strength depend?