A 80 kg fullback attempts to score a touchdown by diving over the goal line. When he is at the goal line and moving horizontally at 6.0 m/s, he is met in midair by an opposing 90 kg linebacker who is initially moving at 4.0 m/s in the opposite direction. The two meet in a head-on collision at the goal line.
a. Does the fullback cross the goal line?
b. What is the collective velocity of the two players after they make contact?