Don, I have no idea what you are saying when you say I haven't figured this out rationally. I was not saying anything about mopeds vs motorcycles, just that if you are going to factor speed into the equation, then make sure you are using the correct equation. Furthermore, the kids that I teach definitely know physics. Most of them take AP physics in high school. I also am an instructor for the Street Survival teen driving program and certainly push the point about speed.
Pretty much every time I take my Puch Maxi out, I do ~60mph (hopefully considerably more this summer), however, when I need to slow down, I have about a mile to do it in. I'm sure glad I don't have to trust my stock rear brakes!