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2D Kinematics Problem, Help Please

  1. Sep 3, 2009 #1
    1. The problem statement, all variables and given/known data
    A particle starts from rest at (r0) = 9m j-hat and moves in the xy-plane with the velocity shown in the figure . The particle passes through a wire hoop located at (r1)=20m i-hat, then continues onward.


    The question I'm having trouble with is finding the y-component of velocity at t=4

    2. Relevant equations

    I think it's v = vi + ay delta t

    3. The attempt at a solution

    I got -40 (express to only one sig fig) and it was wrong, so I have no idea what to do

    Someone please just point me in the direction to go, and not to an older thread
  2. jcsd
  3. Sep 3, 2009 #2


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    The graphs are confusing. Both claim to be of vx as a function of time, but are clearly showing different functions. Can you explain more what the two graphs are supposed to be showing?
  4. Sep 3, 2009 #3
    the first graph (positive V) is Vx the second one is vy
  5. Sep 3, 2009 #4


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    If that graph is the only information we have about vy, your question is unanswerable. Normally you would just read the value of vy at t=4 seconds on the graph. But whoever made the graph has done it sloppily, all we have is the cryptic "4y" label for the velocity at 4 seconds. Plus they mislabelled vx for the graph that should be vy.

    Are these graphs something your professor provided in a printout? I can't believe a textbook would have something like this, since they normally have editors and proofreaders to troubleshoot errors like this.
  6. Sep 3, 2009 #5
    It actually an online site that we do our homework on, I found those graphs elsewhere. I know it has something to do with the acceleration of gravity, but I submitted the answer 40 and got counted wrong (i submitted both negative and positive
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