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Homework Help: Vector displacement problem trouble

  1. Sep 13, 2009 #1
    1. The problem statement, all variables and given/known data
    While vacationing in the mountains, you do some hiking. In the morning, your displacement is S-morning = (1600 m, east) + (3300 m, north) + (160 m, vertical). After lunch your displacement is S-afternoon = (1800 m, west) + (2000 m, north) - (350 m, vertical). At the end of the day, how much higher or lower (in m) are compared to your starting point in the morning?

    2. Relevant equations
    A^2 + B^2 = C^2

    3. The attempt at a solution
    I can't find any other relevant equations that is in the chapter and no examples are given with a third displacement value.

    My attempt in the problem using the same method for both the morning values and after lunch values:

    (1600)^2 + (3300)^2 = C^2
    c = 3667.4 m


    (3667.4)^2 + (160)^2 = C^2
    c = 3670.9 m

    I used the same method for the afternoon values, found the difference between the two (1003.1 m), and it was the incorrect answer.

  2. jcsd
  3. Sep 13, 2009 #2


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    In the morning, how much up you go?
    In the afternoon, from the above point how much down you go?
    So what is the final depth from the starting point?
    The other distances are just distractions.
  4. Sep 13, 2009 #3
    Daniel I think you are misreading the problem, they ask for the change in altitude from your starting point. Assuming that is 0m you just need to add or subtract the vertical distances they give you using say 0m as your starting point.

    Since they give you the changes in vector form you can call the last piece the z axis or K-hat values of the vector and ignore the other dimensions.

    Hope that helps

    If it doesnt then this should be your answer
    0+ 160m - 350m = -190m so your ending altitude would be 190 m less then your starting point
  5. Sep 13, 2009 #4
    I found the correct answer for that part. Now the second part has asked me to: What is the magnitude of your net displacement (in km) for the day?

    I went back to the method I used and just added the separate values for both morning and afternoon. It was the incorrect answer but I figured what I did was reasonable enough to try to find an answer.
  6. Sep 14, 2009 #5


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    Project every displacement on the single plane, then find the net x, y component. z component is known. Find net displacement.
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