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Homework Help: Rho hollow cylinder

  1. Mar 25, 2012 #1
    1. The problem statement, all variables and given/known data

    rho of a hollow cylinder can be found with 4 measured quantity by the folowing formula, proof this formula

    2. Relevant equations

    ρ= 4.m

    d is the outside diameter and D the inside

    3. The attempt at a solution

    since it's my first time ever taking physics classes i'm kinda stuck
    (well first time taking science classes:blushing:)


    so the formula of the hollow cylinder is V=∏.(d²-D²).h

    the 4.m should be the mass but don't realy get what the 4 is standing there for

    Could someone explain me how i should solve this ore give me a helping hand with the beginning of it?
  2. jcsd
  3. Mar 25, 2012 #2


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    Gold Member

    The formula for the area of a circle is

    A = π r2 = (π/4) d2

    where r = radius and d = diameter.

    When you have a hollow circle, the same sort of thing still applies, just with a difference of squares. But notice the (π/4) stays out in front.

    If you think this on through, you will see where the rest of your expression comes from.
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