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Bulk modulus given, find change in P [Fluid Mechanics]

  1. Jan 18, 2016 #1
    1. The problem statement, all variables and given/known data
    If the bulk modulus for water at
    70∘F is 319 kip/in^2, determine the change in pressure required to reduce its volume by 0.3%.

    2. Relevant equations
    E = dP/(dV/V)
    E - Bulk Modulus
    dP - change in pressure
    dV - change in volume
    V - volume

    3. The attempt at a solution
    Well I just said 319 kip/in^2 = dP/(.003/1 in^2) so then dP = .957 kip or 957 lb. But it's looking for an answer using US customary dimensions for pressure. Any ideas? What did I overlook?
     
  2. jcsd
  3. Jan 18, 2016 #2

    SteamKing

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    First of all, units of pounds indicate force, rather than pressure in USCS, which are given in pounds per square inch, or psi, usually.

    Since the volume of the sample is reduced by 0.3%, a pure number without units, then re-arranging the original equation thus:

    ##E = \frac{dP}{dV/V}##

    ##E ⋅ (dV/V) = dP##

    should result in units of pressure, whether they be ksi (= kip / in2) or psi, by suitable conversion.
     
  4. Jan 18, 2016 #3
    I figured it should be, but for some reason I kept getting it as just lb or kip. So would the answer be 957 psi? I only have one attempt left.
     
  5. Jan 18, 2016 #4

    SteamKing

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    Yes.
     
  6. Jan 18, 2016 #5
    Just wanted to say thanks SteamKing for being so helpful, you've answered stuff for me before.
     
  7. Jan 18, 2016 #6

    SteamKing

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    You're welcome.
     
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