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Homework Help: Determine the Acceleration of Collar B as a result of Collar A

  1. Feb 5, 2013 #1
    1. The problem statement, all variables and given/known data
    Collars A and B slide along the fixed right-angle rods and are connected by a cord of length L = 7 m. Determine the acceleration of collar B when y = 2.2 m if collar A is given a constant upward velocity vA = 2.66 m/s. The acceleration of B is positive if to the right, negative if to the left.

    I have attached an image

    2. Relevant equations

    x2+y2 = l2

    3. The attempt at a solution[/b

    I found the distance x, from the base of the support to B to be 6.64529 m

    I took the derivative of the Pythagorean to get:

    2xx' + 2yy' = 0

    Then I took the derivative again:

    2x'x' + 2xx" + 2y'2 + 2yy"

    Solving for x" = -x'2 - y'2 -yy"/x

    x" = -(-yy'/x)2 - y'2/x

    x" = -0.9057

    But it says it's wrong. Where is my mistake?

    Attached Files:

  2. jcsd
  3. Feb 5, 2013 #2


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    (I'm assuming you are using the prime to mean differentiation with respect to time.)

    I'm with you to here, although, for this problem, y'' = 0 .

    This should be
    x'' = (-x'2 - y'2 - yy'')/x

      = (-x'2 - y'2)/x​

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