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Find the Mass of Air in the Room and the Air's Weight

  1. Jan 27, 2013 #1
    1. The problem statement, all variables and given/known data

    The air in a room measuring 8 ft x 9 ft x 12 ft is at 80°F and 1 atm. Determine the mass of the air, in lb, and its weight, in lbf, if g = 32.0 ft/s2

    2. Relevant equations
    1 °F = 460.86°R

    dair = mair/vair

    3. The attempt at a solution

    The air has the same mass as the room, thus mair = 8x9x12

    mair = 864 ft3

    dair = mair/vair

    dair = ρ/RT

    dair = 1 atm/(53.35 ft lb/lbm °R)(540.67°R)

    dair = 3.4668x10-5 atm lbm/ft lbf

    My density seems kinda low. What am I missing? Is it the gc?
  2. jcsd
  3. Jan 27, 2013 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    You should check your units, especially for R.

    A density unit of atm lbm/ ft-lbf makes no sense.
  4. Jan 28, 2013 #3
    Wrong question.
    Last edited: Jan 28, 2013
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