physics

[blackmage_nuke]

for the first formula, using kg i got 12.8 = v2 + v4

Then with coefficient of restitution using this formula i got from wikipedia

which is slightly different to your formula (particularly the bottom)
I got 10(v4)+80 = 72 +9(v2)

then using simultaneous equations with
12.8 -v2 = v4 and
10(v4)+80 = 72 + 9(v2)
(subbing)
i got v2 = 7.15789...
or v2 = 136/19

but i could be wrong, this coefficient of restitution stuff is new to me. I might have gotten some of my negatives in the wrong place too.

I dont think it has anything to do with newtons

edit: you have to be pretty damn good at soccer to kick a ball and hit someone elses ball in mid air