Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Exponential decay with air pressure

  1. Sep 4, 2006 #1
    Air pressure, P, decreases exponentially with the height, h, in meters above sea level:

    P = P0e-0.00012h

    where P0 is the air pressure at sea level.

    (a) At the top of Mount McKinley, height 6198 meters (about 20,330 feet), what is the air pressure, as a percent of the pressure at sea level?

    I think I need to know the air pressure at sea level to answer this question but I'm not given it... Does anyone know it if i need it, and if I don't.. how do i solve the problem without it?

    (b) The maximum cruising altitude of an ordinary commercial jet is around 12,000 meters (about 39,000 feet). At that height, what is the air pressure, as a percent of the sea level value?

    Same question for this one.
  2. jcsd
  3. Sep 4, 2006 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    The air pressure at sea-level is taken as the reference 1 atm of pressure, or 14.696 psia (absolute pressure), or 0.101325 MPa, or 101.325 kPa, 760 mm Hg, or 760 torr (assuming Temp = 25°C/298 K)

    This might be useful for future reference -
    http://www.silcom.com/~aludwig/Physics/UNITS.html - find pressure near bottom of page.
  4. Sep 4, 2006 #3
    so I guess it doesn't matter which units I use?... I suppose atmospheres would be the best to work with.
  5. Sep 4, 2006 #4


    User Avatar
    Science Advisor

    This is why I encourage people to actually Read the Problem before trying to solve it! Then you might notice that the problem asks "what is the air pressure, as a percent of the pressure at sea level?"
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook