1. The problem statement, all variables and given/known data i) Show that when a satellite (or planet) is in a circular orbit it's kinetic energy (positive) is one-half of it's potential energy (negative). ii) Show that in order to escape from the earth you need a speed v=sqrt(2gR) where g=9.8 m/s^2. Neglect Friction and effects of earth's rotation. 2. Relevant equations PE= -GMm/R KE= (1/2)mv^2 3. The attempt at a solution I feel like I'm doing some kind of basic algebra wrong here. I was trying to do part 1 by solving (1/2)KE=PE So, (1/2)(1/2)mv^2 = GMm/R (1/4)v^2 = GM/R v^2 = 4GM/R and v=sqrt(4GM/R) So in the process of trying to find the answer of part 1, I got close to the answer for part 2 (If I had made KE=PE), but now I'm just confused. Is the "1/2" in the equation for KE already accounting for this? Should I be looking at it like mv^2=PE?