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ChE Fundamentals ISSUES!

  1. Feb 1, 2007 #1
    My first assignment in chemical engineering basics class, and already I am having the problems!

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

    A horizontal cylindrical drum is 2m in diameter and 4m long. The drum is slowly filled with benzene (density = 0.879g/cm^3). Derive a formula for W, the weight in newtons of the benzene in the tank, as a function of h, the depth of the liquid in centimeters.

    2. Relevant equations

    We were not given any specific equations, but from attemting to do the solving I use:

    Density = m/V

    3. The attempt at a solution

    I have brainstormed. The volume of the drum is 4(pi)=12.56637. I believe that the problem wants for us to use W(h)=?? when finding the equation, and I understand we want to see that as the benzene increases the container becomes heavier. Also, we have the density.

    Density = (m/V)
    and W=mg, so W=V(density)g

    We could plug things in.

    W=(0.879)(9.8)V and get W=(8.7906)V

    But here is where Im stuck. Does W=(8.7906)V equal W(h)? And should this be a relationship w/time since the benzene is flowing into the drum? I know this could include related rates (calculus) somewhere, but not sure where. Also, where does the drum's volume come in?
  2. jcsd
  3. Feb 2, 2007 #2
    No replies...
  4. Feb 2, 2007 #3


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    Gold Member

    Note the last equation you wrote above.

    You're nearly done. You just need to plug in the equation for the volume of the benzene in the drum.

    PS: No, this has nothing to do with time, since you don't know the rate at which benzene is delivered to the drum.
  5. Feb 4, 2007 #4
    Thank you very so much! It seems I have done some overthinking. I will do that!
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