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Homework Help: Help with pressure-force problem

  1. Nov 29, 2007 #1
    1. The problem statement, all variables and given/known data

    A car misses a turn, sinks into a shallow lake, coming to rest on its side with the door horizontal and at a depth of 13.7 m. If the area of the car door is 0.67 m[tex]^{2}[/tex], what is the force exerted on the outside of the door by the water?

    2. Relevant equations

    Force = pressure * area

    3. The attempt at a solution

    p_total = p_atm + [tex]\rho[/tex] * g * h

    F = (p_atm + [tex]\rho[/tex] * g * h)/area

    F = (101325 N/m[tex]^{2}[/tex] + (1000 kg/m[tex]^{3}[/tex] * 9.8 m/s[tex]^{2}[/tex] * 13.7 m)) / .67 m[tex]^{2}[/tex] = 351582 N

    That's what I've done so far, but it isn't the right answer, can someone help point me in the right direction? I know I did something wrong or forgot something but don't know what it is. Thanks in advance!
    Last edited: Nov 29, 2007
  2. jcsd
  3. Nov 30, 2007 #2


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    Homework Helper

    Maybe the car is still filled with air so that the atmospheric pressure cancels out (it takes some time to fill with water anyway even if the windows are open).
  4. Nov 30, 2007 #3
    No, it tells me to not forget to add the atmospheric pressure.
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