An object travelling at a constant speed and direction may have no acceleration in its own reference frame, true. But it can absolutely accelerate another object in another reference frame.

I don’t know what “F=mv2/2” is but maybe you mean the equation for kinetic energy? KE = 1/2 mv^2

At any rate (ba-dum-tss), getting hit by cars sucks no matter how accurate the mass measurement is. The slower the better.