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Please help me in this homewok

  1. Dec 7, 2009 #1
    1. The problem statement, all variables and given/known data

    A cube 10.0 cm on each edge contains air ( with equivalent molar mass 28.9 gm/mol ) at
    atmospheric pressure and temperature 300K. Find (a) the mass of the gas, (b) its weight,
    (c) the force it exerts on each face of the cube. (d) Comment on the underlying physical reason why such a small sample can exert such a great force.


    ( I know it is simple quastion but i want to sure from my answer )

    please i need the answer today

    best wishes for you
     
  2. jcsd
  3. Dec 7, 2009 #2

    Oddbio

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    Gold Member

    You will need the ideal gas law:
    PV=nRT

    Then write down what you know and your unknowns and see where you can go from that?
    R is a constant R = 8.314472 J/(K*mol)

    your pressure is a known btw, it says it is at atmospheric pressure.
     
  4. Dec 7, 2009 #3
    ok

    i found mass from ideal law

    then

    weight = mg

    ok ?

    now force = P * A right ?

    p = 1 atm = 1.013 * 10^5 N/m^2 . are u sure ?

    then i found F

    ok

    i need comment please
     
  5. Dec 7, 2009 #4

    Oddbio

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    Gold Member

    I don't understand where your getting this from.
    You had the equation right
    Force = Pressure * Area.
    So just multiply the atmospheric pressure by the area of one face on the cube. which is 100cm^2.
     
  6. Dec 7, 2009 #5
    p = 1 atm = 1.013 * 10^5 N/m^2 ( Paskal )

    it is known for evret one

    and we found force in ( Newten ) so we must convert atm to paskal

    now i want the answer for

    (d) Comment on the underlying physical reason why such a small sample can exert such a great force.
     
  7. Dec 7, 2009 #6
    re d) what is gas made up of? what is the average velocity of a gas molecule at 300K? How many are banging into the walls at any one instant? Thats the sort of thing I think is being sought in the answer.
     
  8. Dec 7, 2009 #7
    i don' what you mean

    now see

    i found force and it is equal 1013 newten and it is a great force

    we have small sample of gas that exert this force on each face of cube

    the quastion now .... what is phyiscal reason for that ?
     
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