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Homework Help: Update To My Problem On Vectorcalculus

  1. Feb 9, 2006 #1
    A particle moves in a circle that is centered at the origin. The particle has position r and angular velocity w. The velocity v is given by:

    v = w x r (with x = the cross product).

    My question is, when I calculate this crossproduct with

    w= (d(theta)/dt) k and
    r= x i + y j + z k

    it gives:

    (d(theta)/dt) * x j - (d(theta)/dt) * yi

    Why does this denote the velocity?
  2. jcsd
  3. Feb 9, 2006 #2


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    Science Advisor
    Homework Helper

    Compute its modulus and see whether you can find

    [tex] |\vec{v}|=\frac{d\theta (t)}{dt} R [/tex]

    ,where R is the circle's radius.


    BTW, you can check whether that vector is always tangent to the circle by dotting it with [itex] \vec{r} [/itex].
  4. Feb 9, 2006 #3
    Thanks I get it now :)
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