How to model Kalman filter for Projectile Motion ?

I am experimenting with Kalman filter implementation of Matlab. I wish to model the motion of a ball tossed up by a child in the air using Kalman filter. I have manually annotated the position of the ball in the image frames to use as measurements (ground truth values) for initializing and updating the kalman filter. I have defined the state to be a 6-dimensional vector as follows:

[X Vx Ax Y Vx Ay]

I wish to use 'Constant Acceleration' model. However, I am having difficulty in forming the StateTransitionModel.

Currently the StateTransitionModel Matrix I am using is as follows:

As = [1, 1, 0 , 0, 0 , 0; 0, 1, 1 , 0 , 0 , 0; 0, 0, 1 , 0 , 0 , 0 ; 0, 0 , 0 , 1, 1, 0 ; 0 , 0 , 0 , 0, 1, 1 ; 0 , 0 , 0 , 0, 0, 1 ];

MeasurementModel Matrix is as follows :

Hs = [1, 0, 0 , 0 , 0 , 1];

I am currently not using ControlModel matrix.

The problem with this model is that the acceleration components are currently not being used correctly. If I am to include acceleration components (Ax , Ay) what modifications should I do ?

Also, using the fact that in this case Ay is constant and equal to acceleration due to gravity (g) , How to plug in the value of g ?