Really Tricky Theoretical Probability Question

Hey :)

So, for a school assignment we had to create a carnival game and then calculate the empirical & theoretical probability of it. My game was called 'splat the rat;' basically, I put a computer mouse down a pipe and a contestant had to try and hit it when it came down the bottom. The empirical part was easy; according to it, there is a 47% chance that the mouse will be hit at the bottom. But I'm really struggling with the theoretical aspect; should I find out the average persons reflexes and then calculate the velocity of the mouse going down the pipe and then put them together somehow? If this is on the right track, then how would I find the velocity again? I haven't done science for two years:P

Many thanks!