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Homework Help: Length of tinfoil

  1. May 10, 2010 #1
    1. The problem statement, all variables and given/known data
    Aluminum, which has a mass of 2.7 grams for each cubic centimeter of volume, can be rolled into thin sheets
    which your grandparents probably called "tinfoil." If a lump of aluminum of mass 0.75 kg is rolled into such a
    sheet 18 μm thick and 25 cm wide, approximately how long is this roll of "tinfoil?"



    2. Relevant equations

    v = m/p p = density
    v = L * A
    surface area of circle = 4pi(r)^2
    area of circle = pi(r)^2


    3. The attempt at a solution

    I have spent alot of time on this problem but i can't seem to get it right i do not know what to do with the width or the thickness. I have tried to play it off like the width is the diameter,(which seems possible), but i just don't know what to do i have been working on this problem for 2 days now and i can't figure out what to do with it, please help i have a final on this tomorrow and i see it alot in the old exams so i would like to know how to approach it if the problem gives thickness and width.
     
  2. jcsd
  3. May 10, 2010 #2
    Think about the sheet of the foil before you roll it up. What shape is it?
     
  4. May 10, 2010 #3
    rectangle? so find the area of it as a rectangle ok ha ha don't know why i never thought of that
     
  5. May 10, 2010 #4
    A rectangle yes, but you are interested in the volume since the density is mass over volume.
     
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