I remember this question from years back, the answer is "The unstoppable force goes through the immovable object" The reasoning is that there is a large amount of space between the atoms of materials. The other answer is Nuclear Fission, but that would be if the items in question are destructible.
it depends what the unstoppable force is. it could be wind. it doesnt even have to be fast it just doesnt stop. the unstoppable force would go around the object and continue without stopping. it could even be deflected and go off in another direction, just as long as it doesnt stop.
basically, there are too many variables for there to be a valid answer
they might not interfere with each other, as well as the immovable object might be destroyed, or the source of an unstoppable force be destroyed. That depends on the nature of both the UF and IO.
it is not a paradox! for it to be a paradox we'd need more info! AND, a paradox does not even cause a black hole! black holes are made when a freaking star collapses!