Past exam of the mathematics course of the year 1 of the natural sciences course of the University of Cambridge / 2018 / Paper 1 / 16 / a

The slope of the particle's straight trajectory is $\tan {\theta }_i=y_i/x_0$, soThe endpoint directions $\pm \pi /2$ are parallel to the screen and do not give finite collisions, but each has zero probability in the continuous angular model. The relation therefore holds almost surely.