1. The problem statement, all variables and given/known data Consider two masses of variable magnitude (M m) that are separated by a distance ( r ). Both masses are free to move. Calculate dr/dt. 2. Relevant equations (See below) 3. The attempt at a solution F = GMm / r2 a = Gm / r2 let k = Gm da/dr = -2kr-3 dr/da = (-2k)-1 r3 dr/da * da/dt = dr/dt Just need to solve for da/dt and I don't know how to do that.