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Finding the weight and volume

  1. Feb 3, 2008 #1
    Hi everyone,

    Could someone please help me with this problem?

    1. The problem statement, all variables and given/known data

    A building is 40.0 m X 20.0 m X 11.0 m. The density of air is 1.20 kg/m^3. (A) What is the volume of the building in cubic feet? (B) What is the weight of air in the room in pounds?


    2. Relevant equations
    Density=mass/volume
    1kg is about 2lb
    V=lhw
    1m=3.281ft

    3. The attempt at a solution

    a. (40.0 m)(20.0 m)=
    800.00 m^2
    3
    (8.00 X 10^2 m^2)(11.0 m)=
    8800m^3

    8800m^3(3.281ft/m^3)=
    28872.8=
    28873 or 2.89 x 10^4 ft^3

    b.

    m=(1.20kg/m^3)(800m^3)
    =960 kg
    960kg(2lb/kg)=
    1840 lb

    Could someone please tell me if this is correct and if not show me where I made my mistake?

    Thank you very much
     
  2. jcsd
  3. Feb 3, 2008 #2
    So, I'll start you on part a. The answer is not correct. Whenever you do calculations, it helps to always include all the units and do the same operations on the units as you do on the numeric part. At the end, look at your units and see if that's what you set out to do. Go back and try the conversion again and look at what you have to do to get ft^3 via calculation.

    In part b, where did you get the conversion factor 2 lb/kg? Please recheck that.
     
  4. Feb 3, 2008 #3
    Thank you very much

    Regards
     
  5. Feb 19, 2008 #4
    The weight would just be the volume times the density, right?

    Thank you very much
     
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