two chunks of rock, each having a mass of 1.00kg, collide in space. just before the collision, an observer at rest in the reference frame of a nearby star determines that rock A is moving toward the star at 0.500ci and rock B is moving away from the star at 0.300ci. if the rocks stick together after the collision, what are the direction and magnitude of their velocity (in the reference frame of the star) immediately after the collision?