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Homework Help: Dynamics: 2 block problem

  1. Feb 23, 2016 #1
    1. The problem statement, all variables and given/known data
    Assuming no friction is on the plane or the pulleys and the pulley and rope have negligible mass... Determine the acceleration of each block and the tension in each cord. Block A weighs 100kg, Block B weighs 300kg.
    2. Relevant equations
    ΣF = ma
    ma = 100kg
    mb = 300kg
    3. The attempt at a solution

    ΣFx = max = T1 = 100ax
    ΣFy = may = W - T2 = 2943kg - T2 = 300ay

    I know that I have the relationships right, but I don't know exactly how to extract them...
  2. jcsd
  3. Feb 23, 2016 #2
    What is the relationship between ax and ay? It is constrained motion, so you relate the two accelerations.
  4. Feb 23, 2016 #3
    I think I solved it this way based off of what my professor drew on the board but I need some clarity because I'm not quite sure how this can be...
    if we assume:

    ax = 2ay
    ^My professor's hint

    then we have 4 relations and 4 unknowns. So:

    T1 = 2T2
    100ax = 2[2943 - 300ay]
    50ax = 2943 - 300ay
    ax = 2ay
    50*2ay = 2943 - 300ay
    400ay = 2943

    ay = 7.3m/s^2
    ax = 14.8 m/s^2

    This is an incorrect answer. The correct answer is 8.4m/s^2 for ax which means somewhere my answer is almost 2 times larger.
    Last edited: Feb 23, 2016
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