Dispense with most of the math and think of this question in more practical terms and in an easier to understand way: You have 3 theoretically "perfectly identical", "perfectly symmetrical" cars "A", "B" and "C". If car "A" traveling at "exactly 50kp/h" hits a theoretically "immovable wall" "head on", (that is to say, exactly perpendicular to the plane of their masses) it will undergo, in effect, an "instantaneous deceleration" from 50kp/h to 0kp/h. If the other two theoretically "perfectly identical", "perfectly symmetrical" cars "B" and "C", moving in "exactly opposite directions" crash "exactly head on" (that is to say, coming from exactly opposite points and moving perpendicular to their respective planes of mass and in direct line with the perfect centers of their respective symmetries) at "exactly 50kp/h each", then upon impact they will each transfer 100% of their kinetic energy into the other vehicle and will each undergo, in effect, an "instantaneous deceleration" from 50kp/h to 0kp/h. BY DEFINITION, all 3 vehicles will undergo, in effect, IDENTICAL, instantaneous rates of deceleration! As for the "occupants" of any or all of these cars, they would feel the "effects" of a 50kp/h crash into an immovable object. Remember, of course, this is all happening in the "perfect world" of theoretical physics and the ACTUAL consequences, due to the unpredictability of "real life" physics and its, at times, uncontrolled/uncontrollable variables, might vary SIGNIFICANTLY from those represented above!