physics

[yingao]

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Many automobile air-conditioning systems have the option of using either outside (vented) air in the air cooling system or air recycled from inside the car. Which of the following would best provide rapid and steady cooling of the air in a closed car on a hot, sunny day?

1. use the hotter, recycled air until the inside of the car is cool, then switch to the outside air
2. use the cooler outside air until the inside of the car is cool, then switch to recycle.
3. use recycled air exclusively
4. use the outside air exclusively

I dont know how to do this question, can someone explain the concept please....

 

[wish2bMD]

Is the air initially cooler outside or inside the car? It would take less energy to cool cooler air than hotter air, which is why you find switching to internal air = colder

 

[yingao]

O, I c, thx!

 

[neurodoc]

Many automobile air-conditioning systems have the option of using either outside (vented) air in the air cooling system or air recycled from inside the car. Which of the following would best provide rapid and steady cooling of the air in a closed car on a hot, sunny day?

1. use the hotter, recycled air until the inside of the car is cool, then switch to the outside air
2. use the cooler outside air until the inside of the car is cool, then switch to recycle.
3. use recycled air exclusively
4. use the outside air exclusively

I dont know how to do this question, can someone explain the concept please....

Given that the question states the outside air is "hot" the most efficient cooling would involve recycling the cabin air through the AC system.

 

[MT Headed]

Given that the question states the outside air is "hot" the most efficient cooling would involve recycling the cabin air through the AC system.

I believe this question is relying on the common experience that the inside of a parked, off, closed car is even hotter than the already hot air outside the car.

 

[paul411]

I believe this question is relying on the common experience that the inside of a parked, off, closed car is even hotter than the already hot air outside the car.

Yeah. The answer choices seem to imply this.

2. use the cooler outside air until the inside of the car is cool, then switch to recycle.

This seems like the most reasonable answer because initially the "cooler outside air" is easier to cool (more energy efficient). Once the inside of the car is cool, you don't have to bring in the relatively hotter air from outside and cool that down anymore. You can simply recycle the cooled air in the car.

Where did you find this question?