Does everyone know the stopping distances off by hear from 20 to 70mph, the theory test guide advised I need to know this off by heart, and gives a "handy trick" calculation I can use to work it out, however if I was going to do that when actually driving I'd probably crash.
It's not a practical application that you'd use; The theory test requires you to need to know them. But once you've passed you won't need them.