Curious George observed an interesting event in an international toy exhibition. Two toy cars were moving forward in a monorail. Toy car #1, weighing 10 kg, was ahead of toy car #2, weighing 20 kg, in the beginning, but they collided and joined together. The initial velocity of toy car #1 is 10 m/s and that of toy car #2 is 20 m/s. What is the final velocity of both of these cars after they are connected?Assume that there is no friction in this system.