1. The problem statement, all variables and given/known data How far above the surface of the earth do you need to be for the force of gravity to be reduced to 70% of its value on the surface. 2. Relevant equations g on surface is 9.8 m/s^2 Fg=G*m1*m2/r^2 3. The attempt at a solution Is there a way to do this without knowing the mass of the earth? It seems as though the gravity equation I have above could only be useful if you knew either the mass of the earth or the radius of the earth. I was just wondering if there is a way to approach this without knowing either of those. Thanks!