King and Rook VS King and Pawn: Stopping the promotion

You may encounter such an ending position - you have a King and Rook against King and an A or H pawn.

In some cases tha pawn can be stopped, in others, it can not. It depends on how far advanced the pawn and King are.

Here is a position where it's just too late to stop them and it's a draw.

Whereas here White has a win if the only correct move is played.