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Homework Help: Rates of pressure and volume change

  1. Oct 14, 2007 #1
    1. The problem statement, all variables and given/known data
    A large tank of water has a hose conected to. The tank (a cylinder) is 4.0 m in height and the tank is sealed at the top and has compressed air between the water surface and the top. When the water height h has the value 3.50m, the absolute pressure p of the compressed air is 4.20*10^5Pa. Assume that the air above the water expands at constant temp. and take the atmospheric pressure to be 1.00*10^5Pa. What is the speed at which the water flows out of the hose at h = 3.0m and h = 2.0m? at what value h does the water stop flowing?

    2. Relevant equations
    I'm pretty sure this involves the ideal gas equation of state PV = nrT and maybe the fact that the volume increase or decrease dV with respect to time is equal to the height increase or decrease dh with respect to time....

    3. The attempt at a solution

    I have tried quite a few things but to be honest im stumped at how to approach this problem so please help...i strongly appreciate it...
  2. jcsd
  3. Oct 14, 2007 #2


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    Homework Helper

    Have you had Bernoulli's Equation yet? The fact that the problem asks for the speed of water flow and gives you pressure differences leads me to suspect that they want you to apply that. (Otherwise we'll have to work this out from basic principles...)
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