Final answer:
The brakes do not apply in emergency when cars are properly uncoupled because the air hose, part of the pneumatic brake system, is disconnected, preventing the activation of the brakes.
Step-by-step explanation:
The question implies a physics concept related to the emergency brakes in train cars. When cars are properly uncoupled, the brakes do not apply in emergency because the air hose on both cars is disconnected. This air hose is part of the train's pneumatic brake system, which is essential for engaging the brakes. FIGURE 14.5, described as showing smoking brakes on a truck as evidence of the mechanical equivalent of heat, illustrates that when brakes are applied, friction generates heat, which sometimes results in visible smoke, indicating the energy transformation from mechanical to thermal energy.
When a car is properly uncoupled, it means that it is disconnected from another car or vehicle it was previously attached to. However, this does not mean that the braking system is disengaged. The brakes on each car are separate and independent, so they can still be applied even when the cars are not coupled.
For example, if a driver in the rear car applies the brakes during an emergency, the brakes on their car will still function and help slow down or stop the vehicle, even if it is not coupled to another car.