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Homework Help: Two blocks tied with massless rope sliding down an incline

  1. Oct 4, 2011 #1
    1. The problem statement, all variables and given/known data
    On 20 degree incline, there are two blocks tied together with a rope, sliding down. the block on the top has mass of 2.0 kg (m1) and u_k1(coefficient of kinetic friction for block 1) = .30 the block on the bottom of the incline has mass of 3.0 kg (m2) and u_k2 = .20
    What is the tension of the rope?


    2. Relevant equations
    F=ma, f = F_N*u


    3. The attempt at a solution
    I found F_net for each block by F_net = F_gx(Force of gravity in horiz. direction) - f(friction)
    and got F1_net = .8236 N and F2_net = 4.1754 N
    and because of acceleration constraint, and because block 1 has slower accel, I found accel for block 1, which was .4118 m/s^2 and found F = m2(a) = 1.2354 N
    Because F2_net is larger than F = m2(a), I subtracted those two and got T = 2.94 N which is not correct.
     
  2. jcsd
  3. Oct 4, 2011 #2

    SammyS

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    Draw a Free Body Diagram for each block.

    How did you account for friction?
     
  4. Oct 5, 2011 #3
    I figured it out! I just didn't draw the right free body diagram..

    Thanks!
     
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