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Homework Help: Tension problem, finding acceleration with kinetic friction

  1. Dec 9, 2014 #1
    Three blocks are connected as shown in the uploaded picture. The strings and friction-less pulleys have negligible masses, and the coefficient of kinetic friction between the 2.0 kg block and the table is 0.17. What is the acceleration of the 2.0 kg block?

    2. Relevant equations
    ∑F = ma

    3. The attempt at a solution

    So i wrote 3 newton equations:

    k-T1+T2 = m2a

    T1-m1g = m1a

    T2-m3g = m3a

    Putting them together I got:

    km2g - m1g + m3g = a(m2 + m1 - m3)

    and then tried to solve for acceleration. Problem is every time I do it I end up with a 0 in the denominator so I don't know if I'm doing something wrong conceptually or if I am just messing up in my algebra. I'm also not sure if all three of the blocks have the same acceleration. I would think so since they are all on a string.

    Attached Files:

    Last edited: Dec 9, 2014
  2. jcsd
  3. Dec 9, 2014 #2

    Simon Bridge

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    Science Advisor
    Homework Helper

    Your equation do not match your drawing... but I think I can figure it out.
    m1=1kg, m2=2kg and m3=3kg right?

    The first equation is incorrect - what is the equation governing friction?

    The last equation is inconsistent with the first two - check the direction for positive acceleration.
  4. Dec 9, 2014 #3
    Oh derp.... haha. Thanks.

    I'm looking through my old exams and I'm finding so many little mistakes like that.
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