Question

Pls help me with this simple physics question!!!!​

Answer 1

It happens because at High altitudes pressure of air is less. Hence when mountaineer opens bottle at top of the mountain then lower air pressure traps inside the bottle.

but when mountaineer comes down the mountain air pressure comes back to normal(1 atm) hence bottle having less air pressure inside and higher air pressure outside therefore collapses to much smaller volume.

Hope you understand the answer.