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Homework Help: Board pulled under a box

  1. Oct 15, 2012 #1
    1. The problem statement, all variables and given/known data
    A small box of mass is sitting on a board of mass and length L . The board rests on a frictionless horizontal surface. The coefficient of static friction between the board and the box is . The coefficient of kinetic friction between the board and the box is, as usual, less than .

    Find , the constant force with the least magnitude that must be applied to the board in order to pull the board out from under the the box (which will then fall off of the opposite end of the board).

    2. Relevant equations


    3. The attempt at a solution

    im confused for my force body diagrams
    box is m1 and board is m2
    for the box i have
    Fnet y: n-m1g=0
    Fnet x: fk=m1a

    for the board i have:
    Fnet y: n-(m1+m2)g=0
    Fnet x: F-fk=(m1+m2)a
  2. jcsd
  3. Oct 16, 2012 #2
    Hello, did you try to sketch FBD?

    I thing it might be a problem with Your last line.
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