Deviation from 2D trajectory I need to find out how far a ball is from the predicted trajectory in 2 dimensional space and I know the start and end position of the ball in both dimensions. Along with that I know the initial velocity and the angle at which the ball was launched.  
Every single variable is known in this picture.

The problem is that I can predict where the ball is going to land based on the angle α and the initial velocity v0, but the actual landing is a bit off due to variables assumed to be zero (wind, friction, etc.) and I need a mathematical way of calculating this deviation. 
NOTE: The mathematical model may not include calculus as we haven't covered that part of our curriculum yet. 
Any suggestions on how to do that?
 A: It is worth noting that the force due to air resistance is usually modeled as
$$\vec{F} \propto -\vec{v} \ \ \ \text{or} \ \ \ \vec{F} \propto -|v|^2 \hat{v} $$
Intuitively this makes sense: the faster you go, the more drag you should experience. The minus sign means that the force acts in opposition to the direction you are travelling.
Since the force is proportional to velocity, the force will change at each point in time. Therefore, it is impossible to model drag forces without using calculus. You would need to find the equations of motion and integrate.
That said, as others have mentioned you can just make an estimation of how much error will be introduced by:


*

*not knowing the initial conditions exactly

*ignoring non-conservative forces (friction, air resistance)


The best way to do this is to do the calculation and run the experiment and see how far you are off for a few different sets of initial conditions. That should give you a pretty good estimate of how much your model deviates from reality.
