A5000-kg freight car crashes into a 10,000-kg freight car at rest. they couple upon collision and move with a speed of 2 m/s. what was the initial speed of the 5000-kg freight car? a 5000-kg freight car crashes into a 10,000-kg freight car at rest. they couple upon collision and move with a speed of 2 m/s. what was the initial speed of the 5000-kg freight car? a) 4 m/s b) 8 m/s c) 6 m/s d) 5 m/s e) none of the above