Four railroad cars, each of mass 2.50 X 104 kg, are coupled together and coasting along horizontal tracks at speed vi toward the south. A very strong but foolish movie actor, riding on the second car, uncouples the front car and gives it a big push, increasing its speed to 4.00 m/s southward. The remaining three cars continue moving south, now at 2.00 m/s.
(a) Find the initial speed of the cars.
(b) How much work did the actor do?
(c) State the relationship between the process described here and the process in Problem 18.