1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Piston Pressure and Unit Conversion

  1. Jul 30, 2016 #1
    Problem:
    CO2 is contained in a vertical cylinder at a pressure of 30 atm by a piston with a mass of 57 lbm. If g is 32.4 ft/sec2 and the barometric pressure is 29.7 in. Hg what is the area of the piston?

    Relevant equations
    F = Ma/gc
    W = Mg/gc
    P= F/A
    gc = 32.174 lbm ft / (lbf sec2)
    1 atm = 29.9 in. Hg
    1 atm = 2116.217 lbf / ft2

    Attempt (4 sig figs)
    1)
    29.7 in. Hg * 1 atm / (29.9 in. Hg) = 0.9933 atm
    2) 30 atm - 0.9933 atm = 29.01 atm * 2116.217 lbf / ft2 / (1 atm) = 61,380 lbf / ft2
    3) 61,380 lbf / ft2 = (57 lbm) * (32.4 ft / sec2) / (A * (32.174 lbm ft / (lbf sec2))
    4) A = 9.352 x 10-4 ft2 = 0.1347 in2

    I feel like this number is way too small. Was the assumption that the force of the piston was only its weight on the gas wrong?

    Thanks
     
  2. jcsd
  3. Jul 30, 2016 #2
    I'm pretty rusty on these types of problems, but if I take 60 lb and apply it to an area of 0.001 ft2 (which is 0.144 in2), I get a pressure of 60000 lb/ft2. Your number certainly appears to be in the ballpark.
     
  4. Jul 30, 2016 #3
    Well good to know my answer numerically makes sense. Intuitively though I don't have a clue what something with those dimensions and strength would look like.

    Thanks for the reply!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Piston Pressure and Unit Conversion
  1. Piston Pressure (Replies: 4)

  2. Pressure on a Piston (Replies: 2)

  3. Unit Conversion (Replies: 3)

  4. Pressure in a Piston (Replies: 6)

  5. Unit conversions (Replies: 5)

Loading...