Train car a is at rest when it is hit by train car b. the two cars, which have the same mass, stick together and move off after the collision. how does the final velocity of train cars a and b after the collision compare to the initial velocity of train car b before the collision? a. the final velocity is double train car b's initial velocity. b. the final velocity is the same as train car b'd initial velocity. c. the final velocity is half of train car b's initial velocity. d. the final velocity is zero, since train car b will stop.

The answer will be d. reflects light because it cant be all the others because light cant be other things other than light

You need to be more specific.  i really don't know what a "motion map" is.you can draw a graph of an object's position, distance, displacement, speed,velocity, or acceleration versus time, or you can draw a graph of the object's x-position versus its y-position and not give any information about time at all.if the graph presents position or displacement against time,  then constant velocity is a straight line . . i.e. a line that has  constant slope.if the graph shows speed against time, then constant velocityis a horizontal piece of line.if the graph shows acceleration against time, then constant  velocity is a piece of line that lies on the x-axis . . it's value is zero.