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Friction question

  1. Sep 29, 2007 #1
    A block weighing 8.1 N requires a force of
    2.8 N to push it along at constant velocity.
    What is the coeficient of friction for the

    002 (part 2 of 2) 10 points
    A weight W is now placed on the block and
    4.8 N is needed to push them both at constant
    What is the weight W of the block? Answer
    in units of N.

    For part 1 i used the equation 2.1N = Cf * 8.1N
    and solved for Cf or coefficient of friction

    that was incorrect tho
  2. jcsd
  3. Sep 29, 2007 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Shouldn't that be 2.8 N? (Assuming the force is applied horizontally.)
  4. Sep 29, 2007 #3
    yeah i mistyped that it should be

    2.8N = Friction * 8.1N

    Friction = .34567 ????

    is that correct? if i have that then i can solve the 2nd one

    by taking
    4.8= .345679 *(8.1N+W) and solve for W?
  5. Sep 29, 2007 #4
    and in solving for W there i get 5.7857 N
  6. Sep 29, 2007 #5

    Doc Al

    User Avatar

    Staff: Mentor

    Looks good to me. (You may want to round off your answer to a reasonable number of significant figures--especially if you're using an online system.)
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