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Homework Help: Linkage kinetics problem

  1. Jun 10, 2012 #1
    1. The problem statement, all variables and given/known data

    The linkage ABD is formed by connecting two 8.05-lb bars and a collar of negligible weight. The motion of the linkage is controlled by the force applied to the collar. Knowing that a tthe instant shown the angular velocity and angular acceleration of bar B are zero and 10 rad/s2 counterclockwise, respectively, determine the force P.

    http://img685.imageshack.us/img685/5416/picxv.png [Broken]

    2. Relevant equations

    [tex]\sum \tau = I\alpha[/tex]
    [tex]\sum F = m a_G[/tex]
    [tex]\vec a_G = \vec a_B + \vec a_{G/B}[/tex]

    3. The attempt at a solution

    Considering the vertical bar (1):
    [tex]a_B = \alpha_1 L[/tex]
    [tex]\tau = LF = I\alpha_1 \Rightarrow F = \frac{I\alpha_1}{L} = \frac{mL\alpha_1}{3}[/tex]

    Now, the horizontal one (2):
    [tex]a_{Gx} = a_B = \alpha_1 L[/tex]
    [tex]P\cos \theta - F = ma_{Gx} = m \alpha_1 L \Leftrightarrow P \cos \theta = m\alpha_1 L (1 + 1/3) \Leftrightarrow P = \frac{4m \alpha_1 L}{3\cos \theta} [/tex]

    I know this isn't correct (it doesn't match the solutions), but I can't figure out what I'm doing wrong.

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