# Homework Help: Exponential decay with air pressure

1. Sep 4, 2006

### Jacobpm64

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. Sep 4, 2006

### Astronuc

Staff Emeritus
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.

3. Sep 4, 2006

### Jacobpm64

so I guess it doesn't matter which units I use?... I suppose atmospheres would be the best to work with.

4. Sep 4, 2006

### HallsofIvy

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?"