Conservation of angular momentum problem

[CharlieManfred]

Homework Statement

A proton is shot horizontally at a nucleus on a cartesian plane, a distance B above the nucleus. It is deflected upwards in a hyperbolic path and its path becomes parallel to another ray out of the nucleus, distance A away from this ray. Show that A=B using conservation of angular momentum. Assume that the nucleus does not move and that the collision is perfectly elastic.

Homework Equations

Angular Momentum = Moment of Inertia x Angular Velocity

The Attempt at a Solution

I have no bloody idea where to start.

 

[Mindscrape]

I think energy would probably work too.

Try starting somewhere, otherwise our suggestions will be meaningless.

 

[CharlieManfred]

I can't really try, seeing as I'm completely befuddled. The proton's angular momentum in respect to any point in space isn't constant, because there's an outside bloody force. Trying to use collisions of spherical objects might work, but there's no real R of the nucleus or the proton...Do you think I should just take the cheap way out and do it with laws of symmetry?