Physics
posted by Eden on .
What is the distance from the Earth's center to a point outside the Earth where the gravitational acceleration due to the Earth is 1/20 of its value at the Earth's surface?

m g = G m M / r^2
so
g = G M / r^2
g' = G M /R^2
g'/g = 1/r'^2 / 1/r^2
g'/g = r^2/r'^2
1/20 = r^2/r'^2
so r'/r = sqrt 20 = 4.47
so r' = 4.47 * earth radius 
Thanks for the help, but it said it wasn't right.... I did 4.47*(6.38*10^3)
Is that right? 
earth radius = 6.38*10^6
not 10^3 
28.5 *10^6 = 2.85 * 10^7 meters

this just isnt right...