you could get extremely technical with this. First, you need to find out what type of gear motor ratio you will have. the motor specs will give you the max rpm, and from there, you would have to calculate the acceleration of the "foot" that kicks the ball. (I apologize i don't know the formula). Once you have the acceleration, you could probably somehow measure the angle of acceleration (how high the ball flies as you kick it). From there, all you have to do (neglecting the air pressure of the ball, and the air resistance) is find out how heavy the soccer ball is and you could measure everything else from there. Sorry I don't know the equations for the acceleration of the motor and angle of acceleration, but I'm only in high school myself
haha