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Homework Help: Pressure-water vs gas?

  1. Mar 8, 2012 #1
    1. The problem statement, all variables and given/known data
    In an open U-tube, the pressure of a water column on one side is balanced by the pressure of a column of gasoline on the other side. (a) Compared to the height of the water column, the gasoline column will have (1) a higher, (2) a lower, or (3) the same height. Why? (b) If the height of the water column is 15 cm, what is the height of the gasoline column? [College Physics – Wilson, Buffa, Lou]

    2. Relevant equations
    I guess p=force/area?
    or maybe not?

    3. The attempt at a solution
    I'm really not even sure what this problem is asking...I can't picture the picture that they're trying to depict. If someone could just point me in the right direction, I'd be grateful. Not looking for easy answers, I just don't have a clue what they're asking for really...
    rereading the problem My guess is that the answer to A) is that gasoline will have a higher column. To be applying the same amount of pressure their forces have to be the same and the density of water is greater (1x10^3) than gasoline (726 kg)? So just assuming you'd need more to get a greater force to equalize the pressures?
  2. jcsd
  3. Mar 9, 2012 #2

    Simon Bridge

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    Homework Helper

    They've got a U shaped tube and put water in one side and gasoline in the other side.
    Your equation is correct - the force is provided by gravity... since the two liquids are different densities, what does this mean about the amount of each needed for the balance?
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