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Homework Help: Easy uncertainty question, I need HELP

  1. Feb 12, 2012 #1
    1. The problem statement, all variables and given/known data
    Hey there, I need some help with uncertainties and how to find the speed of a moving object. I have tried to solve the problem several times but my answer seems to be wrong.

    Formula for speed : v=d/t
    My uncertainties: 0.5cm (distance) and 0.5s for time. The uncertainties were measured with the same analog.
    I did the experiment 15 times and got different speed result of the object each time. The total sum of the speeds ( 15 trials) was 44.99s. The average of that is 2.99 (15/44.99)
    Oh and my measuring device was 228cm long (exact)

    I need to find out the speed and the uncertainties
    If I missed any detail please please let me know
    PLEASE HELP!!! I'am very frustrated right now..=S

    2. Relevant equations

    Formula to use : v=d/t
    3. The attempt at a solution

    = (228 +\- 0.5)m/(2.99+\- 0.5)s
    228 divided by 0.5 = 456%
    2.99 divided by 0.5= 5.78%
    456% +5.78%=461.98%

    so now 461.98% * 76.2 ( which I got by diving 288 and 2.99)
    my final answer was v=76.25m? +\- 39%..
    I'am confused..
  2. jcsd
  3. Feb 12, 2012 #2
    Actually spend hours on trying to solve this :S
    Help will be greatly appreciated!
  4. Feb 12, 2012 #3
  5. Feb 12, 2012 #4


    User Avatar

    Check out this site here: http://www.rit.edu/cos/uphysics/uncertainties/Uncertaintiespart2.html [Broken]
    Last edited by a moderator: May 5, 2017
  6. Mar 11, 2012 #5
    Okey, thanks
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