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Homework Help: Fluids - sinking of a can

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

    A cylindrical can of height h and base area A is immersed in water to a depth ho and left to sink down. A small hole of area 'a' exists at the bottom of the base of the can. Determine how quickly the can sinks.

    2. Relevant equations
    Thus, vo = sqrt(2gy)
    AV = avo
    V: velocity of fluid w.r.t. the container

    3. The attempt at a solution

    dy/dt = (a/A)sqrt(2gy)
    or, dy/sqrt(y) = (a/A) sqrt(2g) dt
    or, on integrating from ho to h, i get

    t = sqrt(2/g)[sqrt(h) - sqrt(ho)]A/a

    I am not getting the answer, where did i go wrong.
  2. jcsd
  3. Dec 29, 2007 #2

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    In your diagram, y is shown to be the depth of the bottom of the can from the water surface. Have you taken into account that the pressure inside the can will also increase as the water flows in, thus decreasing the rate of water flow inside. Maybe you have, but why don't you just write the justification for your equation?
  4. Dec 29, 2007 #3
    ah.. thx.. i didn't do that.. i will try to work it out again...
  5. Dec 30, 2007 #4
    i m not able to do ... can you help me with the solution pls
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