A. At the beginning of a typical airline flight you are instructed about the pro

Question

A. At the beginning of a typical airline flight you are instructed about the proper use of oxygen masks that will fall from the ceiling if the cabin pressure suddenly drops. You are advised that the oxygen masks are working properly, even if the bags do not fully inflate.

In fact, the bags expand to their fullest if cabin pressure is lost at high altitude, but expand only partially if the plane is at low altitude. Explain.

B. One of the highest airports in the world is located in La Paz, Bolivia. Pilots prefer to take off from this airport in the morning or the evening, when the air is quite cold. Explain.

C. A drop of water on a kitchen counter evaporates in a matter of minutes. However, only a relatively small fraction of the molecules in the drop move rapidly enough to escape through the drop's surface. Why, then, does the entire drop evaporate rather than just a small fraction of it?

Explanation / Answer

a)the bags expand xpand only partially if the plane is at low altitude due to the fact that it is safe to not use a oxygen mask uopto 10,000 feet and at low altitude , the pressure difference in the cabin atmosphere and the outside air is not that different as compared to at high altitudes.

b)Cold air is denser than warm air and will thus provide more lift when is passes over the aircraft wings. hence causing increase in fuel efficiency and smooth flight due to less turbulence.

c) It is true that only a relatively few water molecules have enough enough kinetic energy to escape in any given microsecond of time. It is also true that when these fast ones do escape, they take with them some energy which will tend to cool the drop (evaporative cooling).   However, this energy is very rapidly replenished by heat flowing in from the kitchen counter, so the drop temperature does not change much.   Thus in the next microsecond of time additional molecules escape and over time the drop is reduced until its dimensions approach the molecular scale. After that things get more complicated.

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