A ball rolls horizontally of the top of a stairway with a speed of 3 m/s. The steps are 20 cm high and 23 cm wide. Wich step does the ball hit first?

To hit the nth step, see how long it has to fall:

4.9t^2 = .20n
t^2 = 0.653n
Now, to land on the nth step, we also need
3t < .23n
See what you can do with that