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Velocity at P

  1. Jan 8, 2004 #1
    Hi. I think this is my 1st post here but I browse a lot on the forum :smile:
    I was trying to know the velocity at a point on a rigid Body (in 2D) and i found this equation on a paper:
    Vap = velocity at point P (body A)
    Va1 = Linear Velocity of the Rigid Body CM (m/s)
    w1 = Angular Velocity of the Rigid Body (rad/s)
    rap with a invers "T" = the perpendicular distance vector from the CM to point p.

    Im working on 2 dimension here so angular velocity is just a scalar

    The question i have is the unreal result that this equation gives to me, for exemple:
    Va1(0, -5)
    rap(-5,-20) -> now we take the prependicular vector (90º to the left)
    rapT(20, -5);
    and if im not mistak making the calculations
    Vap = (0,-5) + ( 1.5*20 + 1.5*(-5))
    Vap = (0,-5) + ( 30+(-7.5))
    Vap = (0,-5) + 22.5 = (22.5, 17.5);
    Vap=(22.5, 17.5)

    I think this value is too high, are my calculations wrongs ?
  2. jcsd
  3. Jan 9, 2004 #2


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    Science Advisor

    Why is that "unreal"? This object is not moving very fast in translation but it is spinning like heck and it's pretty darn big.
  4. Jan 9, 2004 #3
    maybe ur right

    well now that i look better the angular velocity is in rad's!!!!
    lool forgot that
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