Where d₁ is the distance in meters, a is the acceleration of -0.40 m/s² (note the negative sign!), t₁ is the time in seconds, and v₀ is the initial speed across the d₀ = 0 meters starting line (2.81 m/s). Note that a week ago my RipStik runs achieved speeds of 1.60 m/s and -1.56 m/s.
https://www.desmos.com/calculator/avq6o7uk0j