1. The problem statement, all variables and given/known data Two particles of masses M1 = 81000 kg and M2 = 9400 kg are initially at rest an infinite distance apart. As a result of the gravitational force the two masses move towards each other. Calculate the speed of mass M1 and mass M2 when their separation distance is 26.5 km. 2. Relevant equations 3. The attempt at a solution I think you have to use energy-conservation equations here for each mass 1/2mv1^2 - (GM1M2)/R = 1/2mv2^2 - (GM1M2)/R so, for mass M1, v1=0 and (GM1M2)/R on the left = 0 because R = infinite. then you get 1/2m1v2^2 = (GM1M2)/R --and solve for v2, but this doesn't seem to be correct..