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Angular Velocity and Acceleration graph

  1. Apr 14, 2016 #1
    1. The problem statement, all variables and given/known data

    A.) For the graph above what is the angular displacement during the 4 seconds of motion?
    B.) For the graph above what is the angular acceleration from t=2 to t=4?

    2. Relevant equations
    α = at / r
    α = ω / t
    α = Θ / t^2
    ω = Θ / t
    ω = v / r
    Θ = ω t + 0.5 α t^2
    3. The attempt at a solution

    A.) I used ω = Θ / t
    rearranged it to ωt = Θ

    but my issue is what ω do i use? 0, 10, 20? anything in between? And is this even the right equation to use?

    B.) Isn't it not accelerating between t2 and t4? Or is it constant acceleration?
    How i went about it is i used α = ω / t
    since the time is 2 seconds, and the ω is 20. i got 10, but that was wrong :(
  2. jcsd
  3. Apr 14, 2016 #2


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    There is an error in your image, unfortunately.
  4. Apr 14, 2016 #3
    fixed it
  5. Apr 16, 2016 #4
    For the first part it is the area under the graph.
    For the second part the angular acceleration is constant.
  6. Apr 16, 2016 #5


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    Homework Helper
    Gold Member

    Do you know how to find the distance moved from a velocity-time graph?
    Quoting formulae is of little use unless you know what the terms in the formulae represent. E.g. a=v/t is more informatively written as aavg=Δv/Δt. I.e. the average acceleration is the increase in velocity divided by the elapsed time.
    True, but of the choice
    that response could be misleading.
    @df102015 , what do you look at on a velocity-time graph to deduce the acceleration?
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