How can i redirect movement to direction that i need.

So i just creating some kind of fan-made sequel of "Portal 2" logic game made originally by Valve.
I made working portals and they work fine if not include this issue. So while i am dropping object in portal from top and portal is looking on top too it inverts its velocity and its working fine. But when i try to do portals that have angle (Like on walls or on slopes) it still remains vertical velocity. That's problem i need change velocity so it will still be the same but it will have horizontal velocity calculated by portals angle. (I dont need remain vertical speed fully)
How could i make it work like on picture?

 

check this out

should be enough for the project