Here's another link.
http://www.soccerballworld.com/Physics.htm
Right now, we're estimating that we want an initial velocity for the ball of around 10m/s at about 35 degrees to give us... roughly a peak alititude of 1.5m and a flight of 4m... followed by a bounce.
Given a 10cm stroke, that should require a force of about 250N... if we have perfectly elastic collisions of hard bodies. Which... of course, we don't... but our exerimental results are indicating that this isn't a bad first order approximation.
Fiddling around with the formulas a bit more, that would be about 25 joules of work expressed in .01 seconds.... for a very brief power requirement of 2.5kw.
But that doesn't take into account the energy absorbed by the ball, air resistance, the energy required to accellerate the kicking mechanism or any of that... as interesting as the theoretical values might be, they only serve as a mechanism for understanding the empircal values in this type of situation.
Jason