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Homework Help: Solving problem using DE

  1. Jun 19, 2010 #1
    After applying force P, block B accelerates to the right at 3m/s^2
    When B has velocity of 2m/s determine:
    1.The velocity of B relative to A
    2.The acceleration of B relative to A
    3.The absolute velocity of point C

    The image attached show how this works.
    I worked out the total length,L to get

    L = 3(Sb - Sa) + (Sd - Sa)
    so if you differentiate with respect to t you get

    0 = 3 d(Sb - Sa)/dt + d(Sd - Sa)/dt

    then im stuck.

    or is the differential equation supposed to be
    L = 3(Sb - Sd) + 4(Sd - Sa)
    so differentiating would get
    0 = 3 d(Sb - Sd)/dt + 4 d(Sd - Sa)/dt

    because somehow Va=3/4Vb
    if its the second differential equation could someone explain how to get from there to get Va and Vb?

    Attached Files:

  2. jcsd
  3. Jun 20, 2010 #2


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    Science Advisor
    Homework Helper

    hi kiwifruit! :smile:

    (try using the X2 icon just above the Reply box :wink:)
    you're making this very complicated :redface:

    Sd is constant, so use the equation for L to find Sa as a function of Sb :smile:
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