Hi everyone, this is a problem I posted here a month ago but it wasn't given any attention from the helpers here. I still cannot solve it. So I will greatly appreciate any help. 1. The problem statement, all variables and given/known data Three small balls of masses m, 2m and 3m are placed on a smooth horizontal surface so that they lie on the vertices of an equilateral triangle. The masses m and 2m, as well as 2m and 3m, are connected by light inextensible strings. Initially the strings are taut and the mass m is given a velocity v on the surface in a direction parallel to the string connecting 3m and 2m. With what velocity does mass 3m eventually starts moving? (Neglect friction and the mass of the strings.) Refer to http://www.feynmanlectures.info/exercises/three_balls.html for the diagram. 2. Relevant equations I guess it would be the conservation of momentum. 3. The attempt at a solution I wrote down the equation for momentum conservation mv = mv1 + 2mv2 + 3mv3 Anyway I don't even understand the problem in the first place. So I am here to seek help, again.