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Finding actual static friction given mass, external force, and angle.

  1. Sep 29, 2009 #1
    1. What is the actual static frictional force that acts on the block if an external force of 25.0 N acts horizontally on the block? ________N The mass of the block is 25.0kg. Assume g=9.80m/s^2



    2. Relevant equations
    I am using: static frictional force=(coefficient of static friction)(mass)(gravity)


    3. The attempt at a solution
    25N=us(25.0kg)(9.80m/s^2)
    us=0.102

    Of course this is obviously wrong because I am not searching for the coefficient of static friction. Would you be able to guide me to the correct equation for this type of problem?

    4. Other equations I am given
    T=fs, T=Mg, N=Mg


    Thanks,
    Scarlet-
     
  2. jcsd
  3. Sep 30, 2009 #2

    kuruman

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    Is the block moving when the 25 N force acts on it?
     
  4. Sep 30, 2009 #3

    tiny-tim

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    Welcome to PF!

    Hi Scarlet-! Welcome to PF! :smile:

    (have a mu: µ and try using the X2 tag just above the Reply box :wink:)
    The question asks for the force, not for µ. :wink:

    And remember, the actual static frictional force is less than or equal to µN.

    If the block isn't moving, then the horizontal components must add to zero,

    so the friction force must be … ? :smile:
     
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