A fully coloured model of Orbiting Billiard Balls (Nrich 4798).

This worksheet shows a billiard ball (E) on a table. [br][br][b]1) At what angle must the billiard ball be struck for it to return to its start position?[/b][br]Use point "F" to adjust the angle that the ball (E) is struck.[br][br][b]2) Your answer will depend on the length and breadth of the table, but does it depend on where the ball is to start with?[/b][br][br]Don't be too quick to accept this diagram - what assumptions might it be useful to make about the rebound angles?