[mwint]

Think of it this way: the two cars (if they’re the same weight) create a virtual immovable object at the impact point.

“Brick wall” is doing a lot of work there - note that it’s not the same as hitting a stationary car at 50mph, that car would move. We rarely encounter actual immovable objects on or near the road, which is why a 50+50 head-on is more violent than a 50+0 collision into something softer.