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Absolute Uncertainty

  1. Sep 19, 2009 #1
    1. The problem statement, all variables and given/known data
    You measure the mass of a physics textbook to be 2.97±0.07 kg, and use this value to estimate the total mass of 800 identical physics textbooks in the bookstore. What is the absolute uncertainty in your estimate of the total mass?

    I have been working on this for a while. I am not sure why I cannot get it. What I have tried is:

    0.07(2)=0.014 -- since the uncertainty can go up or down .07kg

    then, multiplying the 0.014 by the 800 text books, to get 11.2kg.

    This however apparently is incorrect. What should I do?
  2. jcsd
  3. Sep 19, 2009 #2
    For a value x±dx, in which the error is ±dx, your absolute uncertainty is |±dx| = |dx|. So the magnitude of the maximum error you can get for a book is .07kg. So instead of the .14kg you used, it would be .07kg.

    If what I said doesn't work, then it is probably because you're using 0.07(2) = 0.014...which is not right, its actually 0.14.
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