One car is traveling with a speed of 40 miles per hour. A second car is traveling with a speed of 50 miles per hour. They crash into each other. It is a very different accident if they crash into each other head on, or if the faster one hits the slower one from behind. What does this have to do with the word velocity?

Velocity is a vector whose magnitude is called speed. Collision study needs to analyse the transfer of momentum, which is another vector quantity associated with the velocity vector of each object

Explanation:

The important concept to recall is that velocity is a vector quantity, which has direction apart from just magnitude (as speed is). So in the transfer of momentum (another vector quantity) that takes place in a collision, it is extremely important to know the direction of the velocity vector, since there is much larger transfer of momentum if the cars collide heads on, than if the cars collide from behind while going in the same direction.

c. magnitude and direction