1. The problem statement, all variables and given/known data A 3.000 u (1 u = 931.5 MeV/c2) object moving to the right through a laboratory at 0.8c collides with a 4.000 u object moving to the left through the laboratory at 0.6c. Afterward there are two objects, one of which is a 6.000 u object at rest. Determine the mass of the other object 2. Relevant equations CONSERVATION OF ENERGY [itex]\gamma[/itex]m1c2+[itex]\gamma[/itex]m2c2=[itex]\gamma[/itex]m3c2+[itex]\gamma[/itex]m4c2 3. The attempt at a solution Each gamma is different because of different speeds but for the purpose of time management and the fact that past this I don't know what to do, I left them as gamma. [itex]\gamma[/itex]2794.5Mev+[itex]\gamma[/itex]3726MeV=5589Mev+[itex]\gamma[/itex]m4c2 Am I supposed to assume both objects are at rest? Doesn't seem like that would be the case because the other object would just be 1u. Any thoughts anyone?