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Homework Help: Pulley Question HELP

  1. Aug 6, 2011 #1
    Pulley Question HELP!!

    1. The problem statement, all variables and given/known data

    Blocks A and B are connected by a string passing over an essentially frictionless
    pulley, When the blocks are in motion, Block A experiences
    a force of kinetic friction of magnitude 5.7 N. If mA
    5 2.7 kg and mB
    5 3.7 kg,
    calculate the magnitude of
    (a) the acceleration of the blocks
    (b) the tension in the string

    2. Relevant equations

    Fnet1 = Ft1 - Ff1
    Fnet2 = Fg - Ft1

    Ft1 = Ft2

    3. The attempt at a solution

    m1a - 5.7N = m2g - m2a
    m1a - m2a = m2g + 5.7N
  2. jcsd
  3. Aug 6, 2011 #2


    User Avatar
    Homework Helper

    Re: Pulley Question HELP!!

    You've recognised that the acceleration of both blocks must be the same. That's the most important step.
    I think you may have mixed up your minus signs. It helps to draw the problem, then define for yourself which direction you will take to be positive.
  4. Aug 11, 2011 #3
    Re: Pulley Question HELP!!

    realize that the sum of all forces will always be mass times acceleration. therefor, Find each force affecting block A first and procede by making 2.7a equal to that and then do the same for block B. I'll give you a clue: the forces affecting block A are friction, Tension and gravitational forces. The forces affecting block B are only Tension and Gravitational force. add these up and make then = to ma ad replace m by their mass individually and you should get a good answer.
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