Alright my internet's being retarted and I cannot load the game.
I'm a nerd. I love physics. BUT.. before I can answer your question, I need a couple of answers.

stupid internet.
1) Does the ball accellerate from side to side? (left to right/right to left?)
2) Does anything interfere with the ball's path while it is in motion? If so, it will require more calculations.
3) Are you given enough space and time for you to capture the balls location at 2 instances to calculate it's velocity?
This is very basic physics. If the ball does not accellerate from side to side, then all you need to do is calculate how far it will go in the time that it takes the ball to fall.
You said that you have already gotten the amount of gravity. Good; less for me to explain.
So, You take difference in Y value (height) from the ball to the ground and you calculate how long it will take the ball to fall that distance (with gravitational accelleration...)
Code:
---Formula: //NOTE this ONLY works if you are starting the ball from a height with absolutely NO downward velocity.
t = sqrt((2 * h) / g)
t = time
sqrt = the square root of()
(2 * h) = 2 times the height of the ball (difference in y value)
/g = divided by the accelleration, or gravity.
-----------
All you need to do fill in the approporate variables to this equation and you will have calculated the time it takes to fall.
Now what you need to do is calculate how far side to side it will travel within that given time. If there is no side to side accelleration it is very easy:
Code:
---Formula:
x = v * t
x = distance
v = velocity
t = time
-------------------
However if there is any accelleration you need to use this formula:
Code:
---Formula:
X = (Vo * t) + (1/2 * a * t^2)
x = distance
Vo = original velocity
t = time
a = accelleration
t^2 = time raised to the power of 2.
By doing this you will calculate how far to the left or to the right of the original position the ball will travel BEFORE it touches the ground (where it hits the ground)
If you need further help, PM me and we'll work something out. It's VERY difficult to explain all of this in text.
Hope I helped.
*EDIT*
Waddo:
It is not 9.81Ms^-2... Well it is, but thats typed all wrong and has a completely different meaning to it. The way you typed it, it sounds like it is 9.81 Milliseconds raised to the power of -2.
It is actually 9.8066(rounded to 9.81)m / (s^2). Here it is 9.8066 meters per second squared.

as I said.. I love physics...
