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  1. #1
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    Unhappy 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.)
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  2. #2
    Grand Panjandrum
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    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
    pressure before we can help you with this question.

    RonL

    RonL
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  3. #3
    Forum Admin topsquark's Avatar
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    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
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