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Homework Help: Significant Figures

  1. Sep 26, 2010 #1
    1. The problem statement, all variables and given/known data

    The length of a cylinder is 1.2 x 10^-2 m and its radius is 2.12 x 10^-2 m. What is its volume according to significicant figures?

    2. Relevant equations



    3. The attempt at a solution

    V=(pi)r^2 l
    r^2 = 4.49 x 10^-4 (as radius has 3 significant digits)
    V= 22/7 x 4.49 x 10^-4 x 1.2 x 10^-2
    V= 22/7 x 5.4 x 10^-6 [4.49 x 10^-4 x 1.2 x 10^-2 = 5.388 x 10^-6 = 5.4 x 10^-6 as least no. of significant digits is 2 here)
    so V=1.7 x 10^-5

    Answer is 16.9 x 10^-6
     
  2. jcsd
  3. Sep 26, 2010 #2

    Borek

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    Staff: Mentor

    1.7x10-5 m3 looks correct to me. But you should not use 22/7 for pi nor round down intermediate results.

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  4. Sep 26, 2010 #3
    Intermediate results have to be rounded off in order to satisfy the rules of significant figures.
     
  5. Sep 26, 2010 #4

    Borek

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    Staff: Mentor

    No. You should round them down only if you are displaying them, but you do the calculations using full accuracy.

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  6. Sep 26, 2010 #5
    you mean to say that
    5.388 x 10^-6 = 5.4 x 10^-6
    should be written as 5.3 x 10^-6 ?
     
  7. Sep 26, 2010 #6

    Borek

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    Staff: Mentor

    No, when displaying it should be written as 5.4x10-5, but for calculations you should use 5.388x10-5.

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