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Homework Help: Acceleration of slab

  1. Oct 28, 2011 #1
    1. The problem statement, all variables and given/known data
    A slab of mass m1 = 18 kg rests on a frictionless floor, and a block of mass m2 = 12 kg rests on top of the slab. Between block and slab, the coefficient of static friction is 0.30, and the coefficient of kinetic friction is 0.20. A horizontal force ,F of magnitude 58 N begins to pull directly on the block. What are the accelerations of (a) the block and (b) the slab?

    2. Relevant equations

    3. The attempt at a solution
    Attempts for (a)
    m1*a= F - fk
    Solved for a.
    I got it right.

    Attempts for (b)
    It's sliding (F > Fs) and there is no friction between floor and the slab.
    I assumed the fk is pulling the slab. I put it in this way :
    m2*a = fk.
    Solved for a. But my answer is wrong.

    fk = magnitude of kinetic friction between block and slab.
    I would guess the equation for my (b) or my assumption is wrong.
  2. jcsd
  3. Oct 28, 2011 #2


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    Science Advisor
    Homework Helper
    Gold Member

    Looks right to me. Did you check your math and value for fk?
  4. Oct 28, 2011 #3
    I just checked it. It was right. Thank you for checking, phantomjay.
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