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Homework Help: Relative Velocity Bird Flying Problem

  1. Aug 7, 2006 #1

    danago

    User Avatar
    Gold Member

    Hey. Ive done this question, but my answer is only partly correct according to the answer book. Heres the question:

    "To a bird flying at 20km/h on a bearing of 160 degrees, the wind seems to be coming from the south at 25km/h. Find the true velocity of the wind"

    ok. I said that B is the velocity of the bird, W is the velocity of the wind, and O is the origin. I then found that:

    [tex]
    \begin{array}{l}
    \overrightarrow {OB} = \left( {\begin{array}{*{20}c}
    {20\cos 70} \\
    { - 20\sin 70} \\
    \end{array}} \right) \\
    \overrightarrow {BW} = \left( {\begin{array}{*{20}c}
    0 \\
    {25} \\
    \end{array}} \right) \\
    \end{array}
    [/tex]

    I then said that:
    [tex]
    \begin{array}{l}
    \overrightarrow {BW} = \overrightarrow {BO} + \overrightarrow {OW} \\
    \left( {\begin{array}{*{20}c}
    0 \\
    {25} \\
    \end{array}} \right) = - \left( {\begin{array}{*{20}c}
    {20\cos 70} \\
    { - 20\sin 70} \\
    \end{array}} \right) + \overrightarrow {OW} \\
    \overrightarrow {OW} = \left( {\begin{array}{*{20}c}
    {20\cos 70} \\
    {25 - 20\sin 70} \\
    \end{array}} \right) \\
    \end{array}
    [/tex]

    I then found the answer to be 9.24km/h on a bearing of 48 degrees, but the answer says 9.24hm/h on a bearing of 228 degrees. Have i gone wrong somewhere? is the book wrong? any help is greatly appreciated.

    Thanks,
    Dan.
     
  2. jcsd
  3. Aug 7, 2006 #2

    danago

    User Avatar
    Gold Member

    Ok thanks to anyone who read this and would have helped, but i seem to have solved my own problem :P The answer gave the velocity of the wind coming FROM 228 degrees. The answer i obtained was the wind going TO a direction of 48 degrees.

    Guess id better learn to read properly :P
     
  4. Aug 7, 2006 #3
    oh yay good job 10chars
     
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