A Frictionless Puck of Mass 1

Multiple Choice

A frictionless puck of mass 1.0 kg travels east at 90 m/s toward an initially motionless puck of mass 2.0 kg. When the pucks are 12 meters apart, the speed of the center of mass of the system is

A) 30 m/s.
B) 40 m/s.
C) 60 m/s.
D) 80 m/s.
E) 90 m/s.