The main criteria of a projectile object are:
Projectile Motion for Vertical Velocity Calculator  

Initial Vertical Velocity:
V_{y0} = V_{y} + gt
Acceleration of Gravity:
g = V_{y0}  V_{y} /t
Time:
t = V_{y0}  V_{y} / g
Where,
V_{y} = Vertical Velocity at Time
V_{y0} = Initial Vertical Velocity
g = Acceleration of Gravity
t = Time.
They are under constant acceleration.
There exists a nonzero component which is perpendicular to the acceleration so as to produce a parabolic path. If this condition is not satisfied, the motion is actually a linear motion.
By definition, a projectile has only one force acting upon  the force of gravity.
Example:
Calculate the Vertical Velocity at Time (Vy) for a projectile object by the given details.
Initial Vertical Velocity (V_{y0}) = 40 m/s
Acceleration of Gravity (g) = 10 m/s2
Time (t) = 2 s
Solution:
Apply Formula:
V_{y} = V_{y0}gt
V_{y} = 40 10*2
V_{y} = 40 20
V_{y} = 20m/s
Vertical Velocity at Time (V_{y}) = 20m/s