If the stationary boundary is vertical, vf = [–vix viy] and if the stationary boundary is horizontal, vf = [vix –viy] for incoming velocity vi = [vix viy].
vf = 2 * P + vi
where vi = the incoming velocity and P = the projection of –vi onto the normal of the boundary line.
p = mv
where m = mass and v = velocity.
Impulse = Ft
where F = net force and t = a very small amount of time.
Impulse = Ft = (Δp)
where F = net force, t = a very small amount of time, and p = momentum.
m1v1i + m2v2i = m1v1f + m2v2f
where the 1 subscript represents object 1 and the 2 subscript represents ...