Two Objects of Equal Mass Collide on a Horizontal Frictionless

Multiple Choice

Two objects of equal mass collide on a horizontal frictionless surface. Before the collision, object A is at rest while object B has a constant velocity of 12 m/s. After the collision, the two objects are stuck together. What is the speed of the composite body (A +B) after the collision?

A) 3.0 m/s
B) 6.0 m/s
C) 12 m/s
D) 24 m/s
E) 36 m/s