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Homework Help: Finding the Displacement Vector from 3 Given Vectors

  1. Oct 2, 2013 #1
    My physics teacher has given me a worksheet with several problems involving trigonometry to find a displacement vector from a set of given vectors. Since this is my first year in physics, I feel out of my element and would really appreciate any help or direction given to me on how to go about this problem. It is as follows:

    "A car travels at 65 km/hr for 30 minutes SSW, then 38 km/hr for 45 minutes SW, then 50 km/kr for 25 minutes due W. What is the car's displacement? What is your total distance?"

    I am aware that in order to find the total displacement, you must calculate the distance traveled for each vector and then add them together. I have done that, already.

    I have attempted to put the vectors together "tip-to-tail", but since the tips of the vectors face west, I have sketched a shape where a "parallelogram" is not formed. My physics teacher only showed brief examples of problems where the three vectors can be connected by a displacement vector to form a figure similar to that of a parallelogram. (i.e. you travel 117 km ENE, then 95 km SE, then 298 km SSW. What is your displacement & total distance?)

    Maybe I am just setting the problem up wrong? I've been working on manipulating the vectors to make said shape, but I feel as if that would just alter the displacement from the origin and not give me the correct answer.

    I am not sure where to go from here, and would really appreciate the help since I'm not getting the information needed in class. I accept full responsibility for my confusion, however. Perhaps I'm just over-thinking this "simple" problem?

    Thank you in advance. :redface:
  2. jcsd
  3. Oct 2, 2013 #2


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    Staff: Mentor

    The parallelogram applies when you are adding two vectors. If you are adding more than two, either deal with them two at a time (add two and get a resultant, then add the next vector to that resultant, and so on), or, break all the given vectors down into their individual components at the start and sum the like-components all at once. Combine the resulting component sums into a final resultant vector.
  4. Oct 3, 2013 #3
    I tried this, then asked my physics teacher for some extra help and I ended up not needing it since I got the right answers. Thank you very much for your time, it's really appreciated!
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