A vehicle travelling 30mph collides head-on with another vehicle travelling 50mph, the force of impact, theoretically, would be the same as a vehicle travelling:

Question

A. 80mph hitting a cement wall
B. 80mph hitting a stopped vehicle
c. 50mph hitting a cement wall
d. 30mph hitting a cement wall

Answer 1

What matters in determining impact damage is the relative velocity and whether of not either car (and the center of mass) is free to move afterwards.

That is only true for case B