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Homework Help: Question a/b pressure variation equation

  1. Oct 21, 2011 #1
    Hi everyone, i have a question abuot how my professor is using the pressure variation equation and I would really appreciate help with it!

    1. The problem statement, all variables and given/known data

    How high can you suck water up a strw? The pressure in the lungs can be reduced to about 10 kPa below atmospheric pressure

    2. Professor's Solution

    P=Patm+ρgd --> d=(P-Patm)/ρg --> d=(10 kPa)/(1000 kg/m^3 * 9.8 m/s^2) = 1.0 m

    3. My attempt at the problem

    P=Patm+ρgd --> d=(P-Patm)/ρg --> d=(101.3 kPa-(1atm-10 kPa)/(1000 kg/m^3] * 9.8 m/s^2) =

    What is wrong with my attempt at the solution.

    Another example of my professor's solution is in this problem:
    1. The problem statement, all variables and given/known data

    The maximum pressure most organisms can survive is abotu 1000 times atmospheric pressure. ONly small, simple organisms such as tadpoles and bacteria can survive such high pressure. What then is the maximum depth at whic these organisms can live under the sea (assuming that the density of seawater is 1025 kg/m^3?

    2. Professors Solution

    P=Patm+ρgd --> d=(P-Patm[/SUB)/ρg --> d=(1000 atm)/(1025 kg/m3 * 9.8 m/s2) * (1.013e5 Pa/atm) = 10 km

    Why does 1000 atm= P-Patm[/SUB) ? wouldn't P-Patm[/SUB) be (1000*1 atm)-(1atm)?

    I would really appreciate some help with this problem! Thank you!
  2. jcsd
  3. Oct 21, 2011 #2


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    If the pressure in your lungs can be reduced 10 kPa below atmospheric, what is the difference in pressure between the atmosphere and the inside of your lungs?
  4. Oct 21, 2011 #3
    Thank you very mcuh for your reply

    1 atm - 10 kPa?
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