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Homework Help: Sailboat relative motion

  1. Sep 9, 2016 #1
    1. The problem statement, all variables and given/known data

    Capture.PNG Capture 2.PNG
    2. Relevant equations
    v_theta = r * theta_dot
    1 knot = 1852 m

    3. The attempt at a solution

    v_0 = 6 * (1852m/h) * (1/3600 h/s) = 3.087 m/s
  2. jcsd
  3. Sep 9, 2016 #2


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    Gold Member

    It looks as if the first picture is telling us that the apparent wind is from the W and has a zero N-S component. So the actual wind must have a component equal and opposite to the boat speed, 6 kt blowing from the S.
    In the second picture, the tell tale is responding to 6 kt actual wind from the S, and is feeling 3 kt apparent wind from ahead (6 cos 60). So the
    6 kt wind created by the boat's motion is being reduced by an actual wind of 3 kt from the W.
    Combining these two pieces of information, the actual wind has a component of 6 kt from the S and 3 kt from the W. So a triangle of velocities will give you the answers.
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