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Homework Help: Unit Conversion: What went wrong?

  1. Aug 15, 2010 #1
    1. The problem statement, all variables and given/known data
    Pressures up to 3000 atm are measured with a dead-weight gauge. The piston diameter is 0.17 (in). What is the approximate mass in (lbm) of the weights required?

    3. The attempt at a solution
    Abs. pressure = Gauge pressure + Atmospheric pressure
    = 3000 atm + 1 atm
    = 3001 atm * 14.696 psi/atm
    = 44102.696 psi
    A = pi*D2/4
    = 0.023 in2
    P = F/A
    P*A = mg
    44102.696*0.023 = m * 32.174 ft/s2 (12 in./1 ft)
    m= 2.627 lbm

    4. The actual answer: 1000.7 lbm. So can anyone point out my error?
    Any help would be appreciated. Thank you.
     
  2. jcsd
  3. Aug 15, 2010 #2
    A mass of 1 lbm weighs 1 lbf in standard gravitational field.

    [tex]
    4.41 \times 10^{4} \, \frac{\mathrm{lb}}{\mathrm{in}^{2}} \times (2.3 \times 10^{-2} \, \mathrm{in}^{2}) = 1.01 \times 10^{3} \, \mathrm{lb}
    [/tex]
     
  4. Aug 16, 2010 #3
    Hi, the answer obtained from this should be equivalent to pound force. How about the accelerate force of gravity? Thanks for your comment.
     
  5. Aug 16, 2010 #4
    I don't know what you are talking about. I was not supposed to solve even this much I think. Please use proper English to communicate your ideas.
     
  6. Aug 16, 2010 #5
    I apologise for my broken English. I mean the answer obtained (1.01x10^3 lb) might be lbf instead of lbm. I think acceleration of gravity needed to be taken into account in order to get lbm.
     
  7. Aug 16, 2010 #6
    But, it is taken into account. Did you read this:
     
  8. Aug 16, 2010 #7
    Ok, I will think about it. Thanks
     
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