Hiya. The problem i'm trying to solve is this: I have two cars, each with the same mass. Speed before Collision of Car1 = Xm/s Speed before Collision of Car2 = Ym/s To solve the problem of what speeds the two cars have after an ELASTIC collision, i used simultaneous equations. My process was: make a K.E equation Make a momentum equation Solve for V1, and then thus V2 From my workings, i seem to have found that if the masses of the two vehicles are equal, then in an elastic collision; the speeds afterwards of the two vehicles will just swap. e.g. Both cars' mass = 2Kg Speed of Car1 before collision = +4m/s Speed of Car2 before collision = -2m/s Speed of Car1 after collision = -2m/s = Speed of Car2 before collision Speed of Car2 after collision = +4m/s = Speed of Car1 before collision Will that be the same for all collisions where the mass is the same and the collision is elastic?