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Homework Help: Pressure at the bottom of cylinder immersed in two liquids

  1. May 16, 2012 #1
    1. The problem statement, all variables and given/known data
    A solid cylinder has base area A, height 20 cm and density 0.8 g/cm3, floats in the boundary of oil and water. If the density of oil 0.6 g/cm3, find
    a. the height of cylinder that immersed in oil and water
    b. the hydrostatic pressure at the bottom of the cylinder if the height of oil = 3 times height of cylinder immersed in water

    2. Relevant equations
    P = ρgh
    W = mg
    Fa = ρgV

    3. The attempt at a solution
    a. I am able to do this one. I got the height that immersed in each liquid = 10 cm

    b. So the height of oil = 30 cm. How to find the hydrostatic pressure at the bottom of cylinder? Does the oil give pressure for the bottom part?

    Water will gives pressure at the bottom which is equal to ρgh = 1000 x 10 x 0.1 = 1000 Pa

    I do not know what to do next...I even don't know whether 1000 Pa is the final answer or not...

  2. jcsd
  3. May 16, 2012 #2
    The oil pushes down on the top and also increases the pressure on the bottom pushing up. So if there is 30 cm of oil total, the pressure at the bottom can be determined by adding the pressure due to 30 cm of oil plus the 10 cm of water.
  4. May 16, 2012 #3
    OK thanks :smile:
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