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Homework Help: Bouyant force plastic tube

  1. Apr 10, 2014 #1
    1. The problem statement, all variables and given/known data
    A plastic tube has a cross-sectional area of 5.00 cm^2. The tube is shaped sort of like a "U". The left arm is filled with water until the right arm of length 0.800 m is full of water. The right arm is then sealed with a cap that won't pop off until a force of 9.8 N is applied. What total height of water in the long arm (left arm) will put the seal on the verge of popping?

    2. Relevant equations
    F = ρ*V*g (Force = density * volume * acceleration from gravity)

    3. The attempt at a solution
    Trying to solve for the height h, I used the equation 9.8 N = (5.0 cm2)(1/10000 m2/cm2)(h)(1 kg/m3)(9.81 m/s2)
    I'm using the value 1 kg/m3 as the density of water and 9.81 m/s2 as the acceleration due to gravity.

    Isolating h, I got 1998 m, which seems way to large. I must be doing something wrong. The units work out though. I end up with meters. But the number seems way too large.
  2. jcsd
  3. Apr 10, 2014 #2
    Whoops I figured it out! I should be using a water density of 1000 kg/m^3!
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