The distance for any rectilinear motion at constant acceleration is:
d = v₀t + 0.5at²
where
v₀ is the initial velocity
So, if v₀ = 8v, and it stopped to 0 m/s, then the acceleration is equal to:
a = (0 - 8v)/t = -8v/t
Thus,
d = (8v)(t) + (0.5)(-8v/t)(t²)
d = 8vt - 4t
d = 4t(2v - 1)
