system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why 2 cars of equal mass crashing into each other at 50 mph each is the same as 1 car crashing into a stationary wall at 50 mph, not 100mph.

I would have thought that the cars give 50mph worth of newtons to the other and 50 mph worth of newtons back on itself due to Newton's 3rd law. But I saw the mythbusters  prove that wrong.
gpt
It's all about how quickly the cars in question slow down from 50 mph to 0. This is determined by how much of the impact can be absorbed by the body of the car. A concrete wall absorbs none of it, so a car crashing into one has to do all the absorbing.

Two cars crashing straight into each other (at the same speed) each absorb the force associated with their own momentum, making it equivalent to a single car crashing into a non-impact-absorbing wall.