Question

A ball moving horizontally 3 m/s rolls off the top of flight of stairs. If each stair is 0.5 m high and 0.5 m wide, which stair will the ball hit?

Answer 1

it will hit the 4th stair.
I solved it by trial and hit method.

Answer 2

.... -_-
that's the same way the book tells me, but is there a specific mathematical/physics method to solve it?