What might UTG have here? He may have KJo in which case the 5 is really good for you, or he may have, KK, Kx, JJ, or 55, or J5 (how crazy loose/passive is he?). . . Since he is a passive, this guy capping the flop has something!

I would bet to gain info . . . if he is ahead he will most likely raise. If he has kings up (or worse) and the 5 didn't help him much, he will most likely call. (again, assuming he is passive).

If he calls you will probably win the hand. If he raises you probably lose . . . can you give some expamples/stats at to why you say he is loose/passive? (if he is super passive I would fold to a turn raise, otherwise I call down)