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Homework Help: Block on an incline connected to a mass cord pulley 26˚. acceleration?

  1. Feb 1, 2009 #1
    1. The problem statement, all variables and given/known data
    block 1 lying on an inclined plane is connected to block 2 by a cord passing over a pulley.
    the coefficient of kinetic friction between block 1 and the plane is .21 and block 1 and 2 are 2.6 kg. As block 2 moves down, determine the magnitude of the acceleration of block 1 and block 2 given θ=26˚ (in the diagram, block 2 isnt on a plane, just hanging)

    2. Relevant equations


    3. The attempt at a solution

    we never learned this type of problem in class, but i found an equation in the back of my textbook g (m1sinθ-m2)/(m1+m2)
    i'm guessing m1 and m2 are mass1 and mass2 so when i solved it i got 1.16. this problem is from an online site masteringphysics.com and eventually i guessed 1.8 and it was right, but i'd like to know how to actually do the problem. dont need to answer right away
  2. jcsd
  3. Feb 1, 2009 #2


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    In this problem, the tension in the cord and acceleration of m1 and m2 must be the same. Wright 2 equations, one for m1 and other for m2.
    If a is the acceleration then
    T-m1*g*sin(theta) - mu*m1*g*cos(theta) = m1*a
    m2*g - T = M2*a
    Solve for a.
    Last edited: Feb 1, 2009
  4. Feb 1, 2009 #3


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    There is also the friction force. And the trouble of which way it is acting.
    I get a = 3.66.
    Would appreciate seeing how you get the 1.8.
    Last edited: Feb 1, 2009
  5. Feb 2, 2009 #4
    i really dont even know how to start, our teacher said he might show us on wednesday. he sent this email out to help us because so many people were emailing him questions.
    "replace the mass 2 force with a tension in the connecting rope of 20.7N. This would be the force applied to mass 1. Using this value allows you to solve the problem without any further concern of the effect of moving mass 2 on the acceleration of mass 1. This greatly simplifies the solution of the problem."
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