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Homework Help: Total displacement

  1. Oct 21, 2009 #1
    1. The problem statement, all variables and given/known data
    In a total time of 2.0 min, a duck on a pond paddles 22 m [36 degrees N of E] and then paddles another 65 m [E 25 degrees S]
    Determine the duck's
    i) total distance travelled
    ii) average speed
    iii) total displacement
    iv) average velocity

    2. Relevant equations
    ii) v= delta d/t
    iii) C = sqrt Cx^2 + Cy^2
    iv) still working on it...was focusing on iii) for quite a while

    3. The attempt at a solution
    i) d = 87 m
    ii) v = .73 m/s
    iii)Ax = 22 cos 36 = 17.8 Bx = 65 cos 25 = 58.9
    Ay = 22 sin 36 = 12.9 By = 65 sin 25 =27.5

    Cx = 17.8 + 58.9 = 76.7
    Cy = 12.9 + 27.5 = 40.4
    C = √(〖Cx〗^2+〖Cy〗^2 )
    C = √(5882.89+1632.16)
    C = 86.7
    Therefore, the total displacement is 86.7 m
    I'm hoping I'm at least on the right track...I'm starting an online physics course with absolutely no background. Thanks for any help!
  2. jcsd
  3. Oct 21, 2009 #2

    Andrew Mason

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    Science Advisor
    Homework Helper

    The first rule of vector math is to Draw a vector diagram. In this case, it is a vector diagram of the two displacements.

    You seem to have the right idea but you are making an error in adding the displacements. The y component of the second trip is in the opposite direction to the first. In the first trip the duck goes north. In the second, south. You can see that your answer must be wrong because you have the duck's displacement almost equal to the distance - which would have to be almost a straight line.

  4. Oct 28, 2009 #3
    Thank you for your help ...sorry for the delayed response, I'm apparently quite good at avoiding my physics course LOL. I appreciste the feedback.
    So I ended up with total displacement = 78.1 m after I gave Cy a negative value of -14.6
    Thanks again!
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