This a conservation of momentum problem, gathered from an old textbook. I thought it would be simple, but I seem to be goofing up somewhere in my basic conceptual understanding.
PROBLEM: A 1.0 kg steel ball is dropped from 4.0 m above the floor. It strikes the floor and rises to max height of 2.5 m. Find the momentum transferred TO the floor FROM the ball.
My issues: If I tried to solve it using the $y$ axis as a directional path and take vector sign into account, I end up with the wrong answer. However, if I just take into account the magnitude of the steel ball's $p$ immediately before and after the collision I CAN get the right answer. But I cannot reconcile that with my conceptual understanding. Why cannot I get the right answer when I take direction into account?