In the episode they do three things:
- Crash two cars into each other head-on, each traveling at 50 mph
- Crash a car into a wall at 50 mph
- Crash a car into a wall at 100 mph
Side note: Dad also liked to bring up the Pythagorean theorum whenever possible, taught me to count in binary when I was eight, and convinced me it was very important to memorize at least 10 digits of pi. 3.141592654. Until I was well into high school, I assumed everyone had a parent who did stuff like this.
So anyway, the car that hits the wall at 100 mph is smashed to bits, it's obviously very different from the cars that hit a wall or oncoming car at 50 mph. Reason? Because it takes a certain "equal opposite reaction" to stop a car going that fast... and it takes a very different reaction to stop a car going 100 mph. It doesn't matter where the reaction comes from, it's going to be the same force. The other car is going 50 mph but it gives a lot more than the wall, which is immovable and able to exert a different force just by being where it's at. fun.