I'm trying to figure out a way to determine the force two objects collide in.

I have two vectors defining their linear velocity at the time of impact, their mass and their angular velocity. Keep in mind this is all for a 2D physics engine.

I don't think it's as simple as adding up these values and figuring out if it's large enogh it makes a large impact since that doesn't take into account if the two objects are travelling in the same direction (as an example).

Any ideas?