Vertical Velocity at Time: Vy=Vy0-gt
where, t = Time, g = Acceleration of Gravity, Vy0 = Initial Vertical Velocity, Vy = Vertical Velocity at Time.
For example, when Initial Vertical Velocity = 50m/s, Gravity(g) = 9.8 m/s2, Time(t) = 3s, Vertical Velocity at Time = 20.6 m/s.