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Block Friction Problem

  1. Jun 15, 2009 #1
    1. The problem statement, all variables and given/known data

    A block of mass [tex] M_1[/tex] rests on a block of mass [tex] M_2[/tex] which lies on a frictionless table. The coefficient of friction between the blocks is [tex] \mu [/tex]. What is the maximum horizontal force which can be applied to the lower ([tex] M_2 [/tex]) block for the blocks to accelerate without slipping on one another?

    2. Relevant equations

    3. The attempt at a solution
    The acceleration of the two blocks (assuming they're not slipping) is [tex] a = \frac{F}{M_1 + M_2} [/tex], and you want the upper block ([tex]M_1[/tex]) to not slip, that is, the acceleration times [tex] M_1 [/tex] must be less than or equal to the frictional force. When the blocks start slipping, [tex] M_1 a = \mu M_1 g [/tex] where the frictional force holding the upper block is [tex] f = \mu M_1 g [/tex]. This means that [tex] a = \frac{F_{max}}{M_1 + M_2} = \mu g [/tex], or [tex]F_{max} = \mu g (M_1 + M_2) [/tex].

    I'm not sure if this answer is right, but it makes intuitive sense when looking at the final equation. Thanks for any help!

    [edit] Sorry, posted in wrong section. I can't find a delete button, but any help would still be appreciated
  2. jcsd
  3. Jun 19, 2009 #2


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    Homework Helper
    Gold Member

    Looks correct.
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