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Pressure in a certain tank is 55.8 Pa

  1. Jan 19, 2009 #1
    I am trying to figure if there is anything wrong with this statement.

    The pressure in a certain tank is 55.8 Pa (abs)


    55.8 Pa is about .008 Psi...and the gage pressure would be -100.9 kpa....

    ......I wouldnt think this condition would be possible
     
  2. jcsd
  3. Jan 19, 2009 #2

    mgb_phys

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    Re: pressure

    Depends on the tank, it means it is under (partial) vacuum.
    So ok for a vacuum brake system on a truck - unlikely for a water tank in a house.

    I would check they meant abs rather than gauge and they hadn't missed a prefix on the Pa.
     
  4. Jan 19, 2009 #3
    Re: pressure

    The questions are supposed to be answered True or False stating why its false...or how it could be true....and it states the pressure in Pa (abs)....but i did notice one thing I missed....its -55.8 Pa (abs)....so this pressure would be below a perfect vaccumm which doesnt seem possible to me....


    At zero pressure using absolute pressure you have a perfect vacuum....so can you go below that?

    and the next question says a certain tank has a pressure of -4.65 psig. giving you a absolute pressure of 9.95psi...which I would think would be more of a possiblitly
     
    Last edited: Jan 19, 2009
  5. Jan 19, 2009 #4

    mgb_phys

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    Re: pressure

    You can't have -55.8Pa abs, that's less than nothing = silly.
    -4.65psig = 9.95psi (abs) is true (give or take the odd least sig figure)
     
  6. Jan 19, 2009 #5
    Re: pressure

    Yea thats what i figured for the 55.8 Pa when I noticed the negative sign.....and it would be the same if you had -150 kpa gage which would be -48.9Kpa absolute.....which would = silly again....
     
  7. Jan 19, 2009 #6

    mgb_phys

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    Re: pressure

    Gauge could be -150 kpa if it was between two tanks.
    So one tank with 1000 kPa and another with 850kPa you could have a gauge reading of -150kPa but the question would have to make that clear.
     
  8. Jan 19, 2009 #7
    Re: pressure

    Yea that makes sense...but the question states that its the pressure of one tank...
     
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