1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Pressure at a height

  1. Mar 17, 2013 #1
    1. The problem statement, all variables and given/known data
    (see attachment)


    2. Relevant equations



    3. The attempt at a solution
    I am not sure how to start with this problem. Do I need to use the barometric formula?

    Barometric formula:
    [tex]p=p_0exp\left(\frac{-Mgh}{RT_0}\right)[/tex]
     

    Attached Files:

  2. jcsd
  3. Mar 18, 2013 #2

    ehild

    User Avatar
    Homework Helper
    Gold Member

    Why not?

    ehild
     
  4. Mar 18, 2013 #3
    I tried that but it gives me the wrong answer.
    Here's my attempt:

    Let h=10m, then 2h=20m.
    ##p_{20}=p_0 \exp\left({-\frac{Mg(2h)}{RT}}\right)##
    ##p_{10}=p_0 \exp\left({-\frac{Mgh}{RT}}\right)##

    Let ##\exp\left({-\frac{Mgh}{RT}}\right)=x##.
    [tex]\frac{p_0-p_{20}}{p_0-p_{10}}-2=\frac{1-x^2}{1-x}-2[/tex]
    [tex]=(1+x)-2=x-1[/tex]

    When I substitute the values of all the variable in exponential term, I get ##x-1=-5.6 \times 10^{-4}## but this is wrong. :(

    I used ##M=14 \times 10^{-3} kg/mol##, ##R=8.314 J/(mol \cdot K)## and ##T=293 K##.
     
  5. Mar 18, 2013 #4

    ehild

    User Avatar
    Homework Helper
    Gold Member

    What is the molar mass of nitrogen gas?

    ehild
     
  6. Mar 18, 2013 #5
    Woops, its 28, thanks! :)

    This time I get: ##-1.1 \times 10^{-3}##, is this right?
     
  7. Mar 18, 2013 #6

    ehild

    User Avatar
    Homework Helper
    Gold Member

    Correct.

    ehild
     
  8. Mar 18, 2013 #7
    But when I submit this, it is marked incorrect. :(
     
  9. Mar 18, 2013 #8

    ehild

    User Avatar
    Homework Helper
    Gold Member

    Try more digits.
     
  10. Mar 18, 2013 #9
    Thanks a bunch, yes, it was a problem with significant digits. :)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Pressure at a height
  1. Pressure and height (Replies: 11)

Loading...