How is the air compressor in an air brake system activated?

Answer: B — By engine power and is typically belt-driven

The air compressor in an air brake system is activated by engine power and is typically belt-driven. This means that the compressor is mechanically connected to the engine, often using a belt that transfers the engine's rotational energy to the compressor. As the engine runs, it powers the compressor, which, in turn, compresses air and sends it into the air brake system. This setup is efficient for heavy vehicles like buses, which need a reliable source of power for the braking system to operate effectively under various conditions. The reliance on engine power ensures that the compressor can provide a continuous supply of compressed air as long as the engine is running. The other methods mentioned, such as battery power, solar energy sources, or manual switch control, are not suitable for activating the air compressor in a vehicle's air brake system, as they do not provide the necessary mechanical energy or continuity needed for reliable operation. Instead, those options would be more appropriate for different systems but are not applicable to the air brake compressor's standard operation.