Final answer:
The loss of third rail power on a subway car will first prevent the operation of the train's propulsion system, which is essential for train movement.
Step-by-step explanation:
The loss of third rail power on a subway car will first prevent the functioning of the train's propulsion system. The third rail is a method of providing electric power to trains, and it is crucial for the movement of subway cars. When this power source is disrupted, the motors that drive the train cannot operate, halting the train's movement. Early subway systems, such as the one mentioned in the reference, relied on the third rail to power the trolleys that went underground, thereby avoiding the overcrowded streets and the frequent accidents associated with surface travel.
Moreover, without third rail power, critical systems like lighting, HVAC (heating, ventilation, and air conditioning), and electronic displays within the subway car would also cease to function. However, these systems would typically be secondarily affected as trains are designed with safety measures that ensure basic lighting and emergency systems remain operational for a period of time even after power loss, primarily for passenger safety.