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Homework Help: Problem With Cylinder Involving Mass and Volume

  1. Aug 30, 2012 #1
    1. The problem statement, all variables and given/known data
    There is a cylinder with two sections (not straight down the middle). One has density 4.5(g/cm^3) the other with 6.4. The radius of the cylinder is 6cm and the total length is 19cm. The total mass is 11833 grams. I need to find the length of the lighter density section of the cylinder.

    2. Relevant equations
    A of circle = pi*r^2
    V = B*h
    D = m/v

    3. The attempt at a solution
    I could easily solve this problem if I knew the steps to take. The total volume is about 113 cm^3, but I don't see how I can apply that information. Also, am I correct in thinking that densities cannot be combined? Sorry for the measly attempt, it is just that I am unable to find a way to solve this. The math should be easy. I just need a plan.
  2. jcsd
  3. Aug 30, 2012 #2


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    Science Advisor
    Homework Helper
    Gold Member

    You can write plenty of equations. For example write equations for ...

    1) The mass of the low density part MLD as a function of it's unknown length LLD
    2) The mass of the high density part MHD as a function of it's unknown length LHD

    You can also write v.simple equations such as ones for..

    3) The total mass MTOTas a function of MLD and MHD
    4) The total Length LTOT as a function of LLD and LHD

    Then you will have lots of equations and some unknowns. Solve.
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