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Homework Help: Need help with Physics Vectors, not sure how to do them

  1. Sep 16, 2010 #1
    1. The problem statement, all variables and given/known data

    A girl delivering newspapers travels 5 blocks west, 8 blocks north, then 6 blocks east. What is the magnitude of her resultant displacement? Answer in unit of blocks.

    2. Relevant equations

    Is there an equation for this? I don't think so?

    3. The attempt at a solution

    My attempt is I drew a graph and went 5 to the left, 8 up, and 6 to the right. from there what should I do? Or is that incorrect?

  2. jcsd
  3. Sep 16, 2010 #2


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    That is the correct approach. The resulting displacement is just the sum of those individual vectors. If you drew them to scale, you can connect the starting point to the ending point and measure that vector to get your answer.
  4. Sep 16, 2010 #3
    And if I didnt draw to scale, how could I find it? THanks!
  5. Sep 17, 2010 #4


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    Here's how it works in detail: Each path that the girls takes can be represented by a vector. When drawn out in an x-y coordinate system you can express each vector in terms of its x and y components. The resultant vector is found by adding up all of the x components and then adding up all the y components. You have to be careful to include the signs of the components because those going in the positive direction are plus (naturally) while those going in the negative direction are minus. For your problem you can take north as the positive y direction then south is the negative y direction. You want to take east as the positive x direction and west as the negative x direction. So walking 5 blocks west is -5 in the x direction, while walking 6 blocks east is +6 in the x direction. Add these up and you see she has walked a net 1 in the x direction. Now, I ask you: What is the amount she walked in the y direction?

    You now have enough information to determine the components of her resultant displacement. Using the Pythagorean theorem you can find the length of the resultant vector (her displacement) and with a little trigonometry you can find the angle that vector makes with the x axis.
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