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Homework Help: No idea what to do next

  1. Nov 6, 2008 #1
    given the acceleration
    and knowing that the starting point was (0,0) and that the starting velocity was V0=(-1,0)
    find the Velocity vector and the placement vector
    si what i did was- 1st integral on Ax Ay getting
    Vx= 2t^3-1

    which is fine and is true to the facts- V0=(-1,0)
    but then, 2nd intergal, integral in Vx, Vy
    Rx= 0.5t^4-t
    which is fine, X0=0
    Ry= 1.5PI*cos(0.66PI*t)
    and then Y0 is not 0, i have checked and double checked and triple checked and cannot find my fault, any ideas?/
  2. jcsd
  3. Nov 6, 2008 #2


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    Hi devanlevin! :smile:

    Whenever you integrate, you must include a constant of integration.

    That constant just happened to be 0 in the other parts of the question …

    but it isn't zero here … that's all! :wink:
  4. Nov 7, 2008 #3
    but i did, added Vx0=-1 and Vy0=0, and isnt the constant in this case X0 and Y0, which are both 0 anyway??
  5. Nov 7, 2008 #4


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    Hi devanlevin! :smile:
    ah, I see now …

    No, X0 and Y0 are the "target figures", not the constants themselves.

    You have to choose a constant so that Y(0) = Y0

    in other words, choose C so that 1.5*π*cos(0.66πt) + C = 0. :smile:
  6. Nov 7, 2008 #5
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