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Homework Help: Air pressure needed for ballast

  1. Mar 13, 2010 #1
    A submarine is submerged to a depth of 3150 ft in the Atlantic Ocean. What air pressure (in kpa) is needed to blow water out of the ballast tanks?

    I know the answer is 9410 kpa but I have been going in circles trying to figure this out.

    P=hd using seawater density of 64.0 pound feet cubed did not work for me.

    Thanks for helping:)
    Last edited: Mar 13, 2010
  2. jcsd
  3. Mar 13, 2010 #2


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    Homework Helper

    Let's work in metric units. P=rho*g*h, and you know all three variables, so you can find P. That's the pressure exerted by the water. You have to add on the pressure exerted by the atmosphere, and that's your answer.
  4. Mar 14, 2010 #3
    Thanks Ideasrule:smile:

    P=1000kg/m^3(9.801m/s^2)(3150ft)(1/3.281ft)=9409676.928 pascals= 9410kpa

    I made a mistake and was using 9.81m/s^2 instead of 9.801m/s^2

    I still cant figure out how I got pascals out of kg/m^3 s^2 any suggestions? These type of conversions get tricky.