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Homework Help: A Water Tank on Mars

  1. Nov 3, 2008 #1
    1. The problem statement, all variables and given/known data

    You are assigned the design of a cylindrical, pressurized water tank for a future colony on Mars, where the acceleration due to gravity is 3.71 meters per second per second. The pressure at the surface of the water will be 145 kPa , and the depth of the water will be 14.2m . The pressure of the air in the building outside the tank will be 92.0 kPA. Find the net downward force on the tank's flat bottom, of area 1.80 m2, exerted by the water and air inside the tank and the air outside the tank.

    2. Relevant equations
    P=F/A and P=pgh

    3. The attempt at a solution

    I plugged in P=1000(3.71)(14.2m)
    Then I used that and converted it to kPA to plug in all the pressures combined to find F in the second equation. (52.7+92.0+145)=F/1.80m^2. I got 522. The answer was wrong. Help?
  2. jcsd
  3. Nov 3, 2008 #2


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    Homework Helper

    Hi 12boone,

    You did not mention what the units of your answer of 522 were, so there might be a problem there.

    But the more important thing is that you are not taking into account that the force from the inside pressure pushes down, and the force from the outside pressure pushes up. Do you see what needs to be changed in your force equation? What do you get?
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