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Homework Help: Finding angular velocity of telescopic arm

  1. Dec 4, 2013 #1
    1. The problem statement, all variables and given/known data

    So ,here is the question : The structure is shown in the picture.
    All I need is to find the angular velocity of telescopic arm BC ,in this current position.

    http://img197.imageshack.us/img197/3954/w6e.JPG [Broken]

    2. Relevant equations

    Well,them simple ω=rXv/r[itex]\bullet[/itex]r

    3. The attempt at a solution

    Here is my attempt,and I don't know why it is wrong .

    I said that ω[itex]_{bc}[/itex]=ω[itex]_{b}[/itex]-ω[itex]_{c}[/itex]

    Then I calculated ω[itex]_{b}[/itex]=rXv/r[itex]\bullet[/itex]r , same with ω[itex]_{c}[/itex] .
    The velocity of those points were simply r*ω of the joints.
    I set the coordinates O point in the lower left corner . Anyway,I got the correct angular velocities next to that system of coordinates.
    But when I tried to say ω[itex]_{bc}[/itex]=ω[itex]_{b}[/itex]-ω[itex]_{c}[/itex] , I got the wrong answer .
    Why is that ?
    What is the correct way to look at that problem ?

    Thanks in advance.
    Last edited by a moderator: May 6, 2017
  2. jcsd
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