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Homework Help: Finding the uncertainty of this problem

  1. May 15, 2012 #1
    1. The problem statement, all variables and given/known data

    When a mass of 166.5 ± 3.0 g is added to a spring the spring extends 7.20 ± 0.16 cm.

    What is the uncertainty in the spring constant, k? You may assume g is known precisely with no uncertainty.

    2. Relevant equations

    3. The attempt at a solution

    I just converted the units so 3.0 g = 0.003kg

    and 0.16cm = 0.0016 m

    so to find uncertainty I just did (0.003)(9.8)+(0.0016)

    but that was wrong??

    can someone please tell me what I am doing wrong here?
  2. jcsd
  3. May 15, 2012 #2
    These problems can be quite confusing. In this case, you first find the spring constant with the mass and extention without the uncertainties. Secondly, calculate the spring constant with maximum uncertainty. The next step is up to you.
  4. May 15, 2012 #3
    then find it with minimum uncertainty and divide by 2??
  5. May 15, 2012 #4
    Sounds good to me.
  6. May 15, 2012 #5
    That will just get you the average spring constant, which you already know since the error is symmetric with respect to the average. Instead, the uncertainty is just the difference between the average and the maximum uncertainty one (or the average and the minimum uncertainty one).
  7. May 16, 2012 #6
    would that be the max of mass and extension or just the mass??
    and the average would that be the average of mass and extension?? Thanks..
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