A 5.0-kg mass with an initial velocity of 4.0 m/s, east collides with a 4.0-kg mass with an initial velocity of 3.0 m/s, west. After the collision the 5.0-kg mass has a velocity of 1.2 m/s, south. What is the magnitude of the velocity of the 4.0-kg mass after the collision?
1) 2.0 m/s
2) 1.5 m/s
3) 1.0 m/s
4) 2.5 m/s
5) 3.0 m/s
Answer: 4