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Homework Help: Finding the Length of mercry

  1. Mar 2, 2010 #1
    1. The problem statement, all variables and given/known data

    Au shaped tube has a total length of 1 m, it is initially filled with air at 20* C and 1 atm, mercury is poured in without letting air escape, compressing the air. This continues until the mercury is filled to a level L, how long is L

    2. Relevant equations

    Im guessing PV=NRT,
    It seems like it should involve the density of HG but its not given, nor is the volume

    3. The attempt at a solution

    I don't even know where to start, It seems like the final pressure is needed, Any suggestions?
  2. jcsd
  3. Mar 2, 2010 #2


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    As more mercury is piled on, the length of the air column goes down. This continues until mercury and the compressed air fills the entire tube.
  4. Mar 2, 2010 #3
    I'm still missing something, what does that lead to? Is there a formula Im just not seeing, W/E or ....
  5. Mar 2, 2010 #4


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    Well, it leads to the formula La+Lm=Ltot, where La and Lm are the lengths of mercury and air. You need one more equation to solve the problem; this equation has to relate La with Lm.
  6. Mar 2, 2010 #5
    I don't want to appear dense( no pun intended) but I still don't get it. None of the equations I see are in terms of L, only pressure, velocity or area. I can't see how the youngs modulus would have anything to do with it
  7. Mar 2, 2010 #6
    Does it involve the pressure of mercury as 1 atm is 760 mm HG?
    Last edited: Mar 3, 2010
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