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Maximum Static Force before Blocks Slip

  1. Feb 26, 2012 #1
    An 6.40kg block rests on a 12.5kg block. The interface between the lower mass and the table is frictionless, but there is friction (static friction μs and kinetic friction μk) between the two blocks. A horizontal force F acts on the upper block and causes both blocks to accelerate. The acceleration of both blocks when they begin to slip is 2.0 m/s2.

    fk=μkFN
    fs=μsFN

    I guess I have no idea how to start with this question. Am I supposed to find the normal force first and work from there? Where do I even go from there? Any help would be appreciated, thanks much!
     
  2. jcsd
  3. Feb 26, 2012 #2

    gneill

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    Staff: Mentor

    You haven't stated what it is you're trying to find...
     
  4. Feb 26, 2012 #3
    Aw geez, sorry. I have to find the force at the time when the blocks start to slip.
     
  5. Feb 26, 2012 #4

    gneill

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    Staff: Mentor

    Okay, so immediately before the blocks begin to slip they are essentially one large block...
     
  6. Feb 26, 2012 #5
    Try to imagine by sitting on the lower block. What you see? Where should the force act?
     
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