If you want to use the bullet behavior, the simplest solution would be to set vx,vy in an event above the events I gave, and then setting the bullet angleOfMotion and speed in an event after.
Vx = speed*cos(angleOfMotion)
Vy = speed*sin(angleOfMotion)
Speed = distance(0,0,vx,vy)
AngleOfMotion = angle(0,0,vx,vy)
The other equation you gave was for figuring out the initial speed to stop in a specified distance. From your description you don’t need that. You just need to slow it down.
Global number speed=0
Global number dir=0
For each ball
— set dir to angle(0,0,ball.vx,ball.vy)
— set speed to max(0, distance(0,0,ball.vx,ball.vy)-200*dt)
— ball: set vx to speed*cos(dir)
— ball: set vy to speed*sin(dir)