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Homework Help: Understanding solution method for finding accelerations in a mechanical linkage

  1. May 9, 2016 #1
    1. The problem statement, all variables and given/known data
    I was checking my work and Chegg uses the equations differently. Can somebody tell me why? Maybe I'm misunderstanding how/why to use the equation I chose.
    Steps 1-3.JPG Steps 4-5.JPG

    2. Relevant equations
    They say aB = -ω2ABRB/Ai
    I used aB = aA + αk x r - ω2rB/A

    3. The attempt at a solution
    So obviously mine will be a different answer, I only found aB but it gave me an i and j component because of that cross product. Which one is correct and why? Why can they neglect the cross product?
  2. jcsd
  3. May 9, 2016 #2


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    The cross product term involves angular acceleration of the rod connecting A and B. In the Chegg problem, the angular acceleration is apparently zero.
  4. May 9, 2016 #3
    How do they justify there being no angular acceleration? It doesn't say this is a static situation, so these bars should be rotating towards one another.
  5. May 9, 2016 #4
    I figured it out. The problem states that the velocities are constant and therefore the angular accelerations are zero.
    Man, reading is important. Thank you for explaining this to me!
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