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Book moving and friction problem

  1. Mar 7, 2010 #1
    1. The problem statement, all variables and given/known data


    A BOOK LIES ON A TABLE WHICH HAS WIEGHT OF 8 NEWTON THE COEFICIENT OF STATIC FRICTION BETWEEN THE SURFACES IS 0.4 AND COEFICIENT OF KINETIC FRICTION IS 0.3 (1)HOW MUCH FORCE IS REQIURED TO MOVE THE BOOK(2)HOW MUCH FORCE IS REQUIRED TO MAKE IT MAVE WITH UNIFORM VELOCITY
    2. Relevant equations


    ACCTUALLY I HAVE SOLVED THE QUESTION I JUST WANT TO KNOW THAT IS MOVING THE BOOK AND MAKING THE BOOK MOVE WITH UNIFORM VELOCITY REQUIRE SAME FORCES????
    3. The attempt at a solution
     
  2. jcsd
  3. Mar 7, 2010 #2

    tiny-tim

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    (please don't shout :redface:)

    No, the forces are different.

    What solutions did you get? :confused:
     
  4. Mar 7, 2010 #3

    HallsofIvy

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    Re: Friction

    The force require to "make it move" (initially) is proportional on the static friction. The force necessary to then make it move with uniform velocity is proportional to the kinetic friction. You do the same calculation but in the one case, use static friction and in the other kinetic friction.

    Typically, as here, the coefficient of static friction is larger than the coefficient of kinetic friction so it takes less form to keep an object moving, once you have it started, than it does to make start moving in the first place.
     
  5. Mar 7, 2010 #4
    Re: Friction

    thank you very much now i realised what a silly question i just asked thankx man
     
  6. Mar 7, 2010 #5
    Re: Friction

    the answer to (1)is 3.2 and the answer to (2)is 2.4/SIZE]
     
  7. Mar 7, 2010 #6

    tiny-tim

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    That's right!

    3.2 N is needed to get it moving, but once it's moving, the force can be reduced to 2.4N for steady speed. :smile:
     
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