What happens to the brake shoes as a result of a forced-out brake cylinder piston?

When a forced-out brake cylinder piston occurs, it pushes the brake shoes into contact with the wheels. This action is crucial for the braking process in a train. As the piston extends, it creates a mechanical movement that causes the brake shoes to press against the wheel surfaces, generating friction, which is necessary for slowing down or stopping the train.

This response directly relates to the functioning of an air brake system, where the application of air pressure to the brake cylinder piston activates the brakes by forcing the shoes against the wheels. Such a mechanism is fundamental for effective train control and safety during operation. The other choices do not pertain to the mechanical action resulting from a forced-out piston, as they either describe conditions that do not occur due to this action or focus on maintenance and inspection rather than the immediate result of brake application.