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Air Pressure + Water formula

  1. May 31, 2006 #1
    is there a formula which i can use to determine the the velocity of an object propelled by a gas under compression and a fluid?
    thanks
    Pavadrin
     
  2. jcsd
  3. May 31, 2006 #2

    Andrew Mason

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    Can you clarify? What exactly is the problem you are trying to solve?

    AM
     
  4. Jun 1, 2006 #3
    Im given a conatainer at a set volume, with an amount of water which is given to me, both in volume and mass. I need to work out the amount of thrust which this vessel could expel, exculding the aerodynamics of the vessel.
    thanks
     
  5. Jun 1, 2006 #4

    Andrew Mason

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    The thrust is given by dp/dt = vdm/dt where dm/dt is the time rate of change of mass of the system.

    ?? Why not just give us the problem? Is there air in the container? Are you given the pressure?

    AM
     
  6. Jun 2, 2006 #5
    okay the problem is as follows:
    In a container with the volume of 1.5L, 500mL of water is introduced, as well as 100psi of air pressure. Calculate the amount of thrust this vessel will be able to provide if the air and water is allowed to escape through a 5mm opening.
    if nobody is able this question, don't stress, and sorry for an inconveniences which may have been a result of my bad post.
     
  7. Jun 2, 2006 #6

    Andrew Mason

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    Assume that the water covers the hole. What is the speed at which water will be ejected through the hole? (Hint: look up Bernouilli's equation). Then determine the rate at which mass (water) leaves the container. Then just use F = dp/dt = vdm/dt to determine the thrust.

    AM
     
  8. Jun 3, 2006 #7
    thanks Andrew Mason, ill shall look up the suggested equation and then re-post if i encounter more problems.
    thanks once again,
    Pavadrin
     
  9. Jun 3, 2006 #8
    im not sure on how to apply Bernouilli's equation. What I found on the internet about this eqaution is:change in pressure+change in kinetic energy/volume=0. I do not know how to calculate kinetic energy, but I do know that potential energy loss=kinetic energy gain. If what I have sated about Bernouilli's equation is correct, then I have calculated the change in pressure as being 588.2 kPa or 85.308 Psi, (assuming that the atmosphere pressure outside of the container is 101.3 kPa)
     
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