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Homework Help: Quick 2D Motion Question (wind resistance)

  1. Oct 4, 2012 #1
    1. The problem statement, all variables and given/known data
    An airplane is flying 100m/s (N20E) according to the pilot, but is in a wind that is blowing 40 m/s (S10E). What is the plane's real velocity?

    2. Relevant equations
    Pythagorean Therom
    Cosin and Sin Laws
    Component Method

    3. The attempt at a solution

    Okay, I think I can easily get the answer if I know what this question is asking me. By real velocity, Does it mean the displacement from point 100 m/s (N20E) to 40 m/s (S20E)? Like, I can draw it on a graph and make the triangle. I would then calculate the angle and length of the unknown side. If that's not it, Then how would I go about getting it? Please Help me understand this.
  2. jcsd
  3. Oct 4, 2012 #2


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    Hi Vroc! :smile:
    It means the velocity Vpa of the plane relative to the air is 100 m/s (N20E)

    you're given Vag, the velocity of the air relative to the ground,

    and you need to find Vpg, the velocity of the plane relative to the ground. :wink:
  4. Oct 4, 2012 #3
    What? I just need to know what formula to use or how I can use my graph to find the answer.
    I'm given the planes Velocity (100m/s n20e) and than the wind (40 m/s s10e)
  5. Oct 4, 2012 #4


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    no, that's not the plane's velocity (relative to the ground), it's the plane's velocity relative to the air

    now use vector addition
  6. Oct 4, 2012 #5
    Okay, If I can use vector addiction, than I can do it the way I mentioned earlier by making a triangle and finding the unknown side and angle because they both are ways of finding the same thing. correct?
  7. Oct 4, 2012 #6


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    correct :smile:

    (and make sure your vector triangle has the arrows the right way round,

    so that Vpg = Vpa + Vag :wink:)
  8. Oct 4, 2012 #7
    Thank you so much.
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