1. The problem statement, all variables and given/known data Car 1 weighing 1000 kg crashes into the rear of parked car 2 weighing 1100 kg and stops. Car2 moves ahead 2 ms2. What is the velocity of car1 at impact? 2. Relevant equations (m1v1+m2v2)=(m1v3+m2v4) 3. The attempt at a solution (m2V4)/m1 (1100*2)/1000 2.2ms2= 2200/1000 Okay, now I know this is right, but what I don't know is how do they arrive at the equation (m2v4)/m1 ????