Ricochet into the back of the vehicle? <ROTFL>
Being forcefully thrown? I assume you mean by the cops--it would be pretty hard for them to throw him against the back of the vehicle.
Acceleration? Large vehicles usually have pretty poor acceleration.
Poor in what sense? A Ford E350 has a 0-60 time that's about on par with a 60k 3.5L Mercedes Benz's 0-75. I rented one when I was hauling bricks to make a barbecue in my old place. Honestly, if that thing had an A-Team paint job I wouldn't have minded cruising around in it.
Even if the knife is legal it is not a crime to arrest someone for having a knife that later turns out to be legal.
Probably cause would have to exist apart from simply owning a knife that may or may not be legal (a la DeBerry).
Except we have different charges for what the intent was. Normally for murder you would have to show that their intent was to kill the person where if it was a rough ride the intent would be to hurt or scare the person.
If the intent was to harm him and not necessarily kill him but he had a preexisting condition that turned the harming into a killing then that would be sufficient to meet the requirement for mens rea. If someone has hemophilia, gets punched in the nose, and bleeds to death before medical intervention can provide help an argument from the aggressor that they only meant to injure would be laughed at on its face.