Answer :
Final answer:
The air pressure in the service line of a tractor-trailer with coupled air brakes is the pressure applied by the hand valve or foot valve, an important pneumatics concept related to vehicle safety and operation.
Explanation:
The question pertains to the air pressure present in the service line of a tractor-trailer air brake system. With the tractor and trailer coupled, the air pressure present in the service line corresponds to the pressure applied by the hand valve or foot valve. This system is crucial for vehicle safety as it controls the air brakes used to slow down or stop the trailer. Understanding the principles of pneumatics and the characteristics of gases under pressure is essential in various real-world applications, including the operation of air brake systems in large vehicles.
