1. The problem statement, all variables and given/own data http://prntscr.com/661d5d 2. Relevant equations m1v1 + m2v2 = m1v1p +m2v2p 3. The attempt at a solution I asumed that the momentum in the y direction is constant, and that in the x direction it is conversved. Also, i thought of it as 2 parts to this problem. The momentum of the first cart plus that of the rock has to equal the combined momentum. This combination plus the negative momentum of the 2nd cart, must equal the desired velocity of the entire system. I dont think this logic is correct since i didnt get the right answer, so clarification on that should help me solve the problem. anyway here's the math (x direction) Vrx = 1.20cos30 Mc1Vc1 + MrVr = McVc1f + MrVrf * here i assume that the final velocity is going to be the same for both of them. plugging in the values i get this Vf=300/(Mc1 + Mr) Vf = .75m/s Now, the the momentum of the entire system should be equal to the rock and the first cart minus the second. (Mc2+Mr)Vf - Mc2Vc2 = M(system)V(system) I get V = .359 Ans : .205 m/s Any help is appreciated, thanks!