# Puzzle #14 – Cue the Queue

Imagine an infinite row of regularly spaced billiard balls. The diameter of the balls is $d$ and their centre-to-centre distance is $D$. The centres of the balls lie on a common axis.

You strike the first ball at a small angle $\theta_0$ to the axis. The balls collide elastically.

Question: Assuming the balls are signficantly further apart than they are wide, after approximately how many collisions between balls is the chain broken?