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Homework Help: Absolute Uncertainty question! Help!

  1. Jan 29, 2012 #1
    1. The problem statement, all variables and given/known data

    Lab 1: Question 6. (Note: each time you do this problem, the numbers will be different.)
    I want to measure accurately the time it takes for the drum of my clothes dryer to make one rotation. Since the door on the dryer is made of heat resistant glass, I can see the drum rotate. I take my stopwatch, start it when a visible mark on the drum gets to the up-most position, and stop it when the visible mark on the drum returns to the up-most position after making 19 rotations. I estimate that my reaction time limits the accuracy of both my starting and stopping the stopwatch to 0.2 s. I measure that the 19 rotations take 18 s.

    First, what is the error in my measurement of 19 rotations?

    Second, what is the time it takes for one rotation and its absolute uncertainty (same as absolute error)?

    2. Relevant equations

    (not sure)

    3. The attempt at a solution

    For the first part of the question, I found the error in the measurement to be .28 s (which is correct) . However, I can't figure out the time it takes for one rotation and its uncertainty. I have gotten multiple answers such as 1.033 and 1.039 and 1.077. (all wrong)

    Please help!
  2. jcsd
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