easy, but I'll give the other people a hint: When you calculate for a 2-d collision

you calculate for the normal vector and a tangent vector like how Professor Hwang

had done "Va1 and Va2 were calculated using the normal vector and Vb1 and Vb2

were calculated using". When you are calculating for a 3-d collision you have to

find i second tangent vector and just adjust the equations professor has to inclue

the z direction in (x, y, z). If you require more detail for an elastic 2-d collision

equations use the following site: [url=http://www.geocities.com/vobarian/2dcollisions/2dcollisions.pdf]http://www.geocities.com/vobarian/2dcollisions/2dcollisions.pdf[/url]

Please correct me if I am wrong and than-you.