Question

Air in the cabin of an airliner is usually kept at a constant temperature and pressure. State with a reason , the change if any to the internal energy of the air in the cabin

* as a result of traveling at high altitude
change : ______________
reason : _________________

Answer 1

@Dan.Harrison

Answer 2

The statement in the question is wrong for a start. Pressurised cabins are not kept at constant pressure. It decreases as the aircraft climbs, which is why your ears pop and bags of crisps explode but whatever.

Are you given a particular formula for internal energy?
Maybe something like
\[U = nC_VT\]
but I'm not sure that one will help much.

The things that can change in a pressurised cabin kept at constant temperature and pressure are volume (expanding against decreased external pressure) and the amount of gas (pumps are used to inject gas into the cabin).

I'm sure you know
\[PV = nRT\]

Well, P, R and T are fixed, but V and n are not. It seems like if V were increased, n must be increased otherwise either T or P would change.

So I guess you need to know how internal energy is changed by n and V with constant everything else.

Answer 3

hey @broken_symmetry , thank you for your detailed explanation about this. Well, actually the question doesnt need that big explanationn for the answer. I mean we just have to state if the internal energy ( kinetic energy + potential energy) will increase or decrease or just stays the same along with a reason concerned about the changes happened to whether potential energy or kinetic energy .

Answer 4

Broken, the volume of the aircraft will remain constant the aircraft will not change size during flight. To Keep constant pressure air is pumped into the cabin continuously and that compressed air is cooled because using the gas laws the air becomes super heated due to being pressurized.

Answer 5

Metal structures can expand, but yeah I admit it'll be negligible.