To explore the difference between crashing a car at 70 mph and 85 mph, I will use a model. This car doesn’t have a crumple zone, it has a huge spring on the front. Here is a diagram.
I think I can do this without picking a mass of the car. Suppose that I have a car going 70 mph (31 m/s) and it crashes into a wall with a spring compression of 1 meter (I just randomly picked that). What would the value for m/k be?