Question

Consider an automobile traveling at a constant speed along a road. Determine the direction of the heat and work interactions, taking the following as the system: (a) the car radiator, \((b)\) the car engine, \((c)\) the car wheels, \((d)\) the road, and \((e)\) the air surrounding the car.

Short answer

Answer: (a) The car radiator has heat transfer out of the system to the surrounding air. (b) The car engine has work transfer out of the system and heat transfer out of the system to the radiator. (c) The car wheels have work transfer into the system and minimal heat transfer with the road. (d) The road has work transfer out of the system from the car wheels and minor heat transfer from the wheels. (e) The surrounding air has heat transfer into the system from the car radiator.

Step-by-step solution

(a) The car radiator

The radiator's main function is to dissipate heat produced by the car engine to the surrounding air. In this case, the heat interaction is from the radiator to the surrounding air (heat transfer out of the system).

(b) The car engine

The engine of the car performs work on the wheels and other systems in the car in order to maintain its constant speed. This means there is work being done by the engine (work transfer out of the system). Additionally, the engine generates heat as a result of combustion, which is then partially transferred to the radiator to be dissipated. Therefore, we have heat interaction from the engine to the radiator (heat transfer out of the system).

(c) The car wheels

The wheels receive work from the engine, allowing the car to maintain a constant speed. This means work interaction is taking place into the wheels from the engine (work transfer into the system). There might also be some minimal heat transfer taking place between the wheels and the road, but this contribution would be small compared to the work interaction.

(d) The road

The road experiences a force from the wheels, which results in work being done by the wheels on the road. This implies work interaction from the car wheels to the road (work transfer out of the system). Additionally, a small amount of heat might be transferred from the wheels to the road, but this contribution would be minor compared to the work interaction.

(e) The air surrounding the car

The air surrounding the car mainly acts as a heat sink for the car radiator. This means heat interaction is taking place from the radiator to the surrounding air (heat transfer into the system). Furthermore, as the car moves through the air, it generates some air resistance, but this mainly affects the work done by the engine and not the heat interactions with the air.