I've been searching around the internet and there doesn't seem to be a straight answer for this. People just spit out an answer and don't back it up with any explanation. This is a complex situation in real life, so let's assume both cars are of the same mass and simplify the scenario by assuming the simplest collision with no fusion of the two cars into one mass etc. Although this is a simplification of the real life scenario, i am curious if the energy to stop a car going 120mph that hits an immovable wall is equivalent to the energy to stop one of the two cars (each going 60mph) that collide and both stop at the collision point. Can anyone show this using physics formulas?