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Homework Help: 2D motion finding displacement direction and velocity

  1. Sep 16, 2008 #1
    1. The problem statement, all variables and given/known data
    some one walking three directions 0.35 east then 0.75 south then 2.95 33 degrees north of west. The whole trip took 2 hours. Magnitude and direction of displacement as well as the magnitude and direction of velocity.

    2. Relevant equations
    r (displacement vector) x (I think in the equation it's the x components) y ( y components) a and Im confused with the x^ and y^ the hats are supposed to be on top. The equation is r=xx^+yy^ where x=d1-d3cos(theta) and where y=-d2+d3sin(theta) where the d's are distance one = 03.5 distance two =0.75 and distance 3 = 2.95

    3. The attempt at a solution
    so I solved the equations of x and y and for x I got -2.124 then for y I got 0.856 then I pluged those into the other equation and got 1.606 which i thought would be the magnitude but it was not correct and I don't really know what to do with the x^ and y^ or how to find the direction of this displacement any help would be great
  2. jcsd
  3. Sep 16, 2008 #2
    Actually showing your work step by step for how you got your anwers would be helpful.
  4. Sep 16, 2008 #3
    ok so for the x equation I put x=0.35-2.95(cos(33)) then I put that in my calculator and got the answer I gave then for the y equation I did y=-0.75+2.95(sin(33)) and got y=0.856 then in the other equation where I'm finding r I just added those two numbers together because I don't know what to do with the x and y hats . . . Im retarded
  5. Sep 16, 2008 #4
    You're not retarded. Don't say that.

    The hatted characters are just there to indicate the direction of the component of the vector. In the 2D case, the magnitude is found by using the pythagorean theorem with the components you found as the legs of the triangle. It should be smooth sailing from there.
  6. Sep 16, 2008 #5
    ok so I used the pythagorean theorem and got the right answer for the magnitude of the displacement, but how do I find the direction of the displacement
  7. Sep 16, 2008 #6
    and I found the velocity but also do not know how to find the direction is it the inverse tangent of the angle 33 with the x and y components I found?
  8. Sep 17, 2008 #7
    It's the inverse tangent of y divided x. Be sure you have the correct signs on the components.
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