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Homework Help: Stacked blocks problem

  1. Oct 4, 2014 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations
    F= ma

    3. The attempt at a solution
    X does not slip. so friction exists. Friction should be equal to the force F applied so that according to Newton's 3rd law, the friction and F cancel out and X remains on Y.
    Is this the right concept?
  2. jcsd
  3. Oct 5, 2014 #2


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    Homework Helper

    No. F is applied on Y. The friction between X and Y acts also on X. So the net horizontal force exerted on Y is F-friction. If F and the friction cancel out Y does not accelerate. As X moves together with Y the whole system stays in rest or moves without acceleration. But the problem stated that it accelerates.
    X does not slip on Y means that they move together, with the same acceleration.
  4. Oct 5, 2014 #3

    Simon Bridge

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    Science Advisor
    Homework Helper

    That would be fine if the boxes moved at a constant speed ... but they don't.
    Instead, draw a free body diagram for each block.
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