# Help me!

• Jul 25th 2006, 04:32 PM
babygirl
Help me!
What is the fractional decrease in pressure when a barometer is raised 35 m to the top of a building? (Assume that the density of air is constant over that distance.)
• Jul 25th 2006, 07:55 PM
CaptainBlack
Quote:

Originally Posted by babygirl
What is the fractional decrease in pressure when a barometer is raised 35 m to the top of a building? (Assume that the density of air is constant over that distance.)

There is insufficient information in this problem to solve it.

If this was my problem I would look up in my text book or do a google search
for the altitude dependence of air pressure (giving priority to my text book
or what I have been told by my teacher).

There I might find air pressure drops by about 1 part in 1000 for every 8m
increase in altitude, for altitudes of less than a few hundred metres.

Alternatively you might find that the half height of the atmosphere for air
pressure is ~5000m

We really need to know what you are supposed to know about atmosheric

RonL

RonL
• Jul 26th 2006, 05:01 AM
topsquark
Quote:

Originally Posted by babygirl
What is the fractional decrease in pressure when a barometer is raised 35 m to the top of a building? (Assume that the density of air is constant over that distance.)

As CaptainBlack mentioned, I'm not sure of what you are using for your constants, but in general:
$P = P_0 + \rho g \Delta h$

so the fractional decrease would be
$\frac{\rho g \Delta h}{P}$.

(I'm presuming P is at sea level.)

-Dan