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Homework Help: Maximum Parallel Force of an Object

  1. Nov 22, 2006 #1
    "For a 7.5 kg object on a horizontal surface that has a coefficient of static friction where us = 1.0, and a coefficient of kinetic friction where uk = 0.8, the maximum parallel force which will not set the object in motion is?"

    a) 23.5 N
    b) 51.2 N
    c) 60.0 N
    d) 73.5 N
    e) 81.3 N

    This is the first problem I've ever done with the coefficient of static and kinetic friction. I have these formulas; F fr = ukFN; Fmax = usFN

    Im not sure if thats all I need. I do know that the Normal force (FN) is 71.8, but Im not sure how to go about finding the "max parallel force". If I solve for "Fmax" I get 71.8, but that leaves out the coefficient of static friction. I think I need help
  2. jcsd
  3. Nov 22, 2006 #2
    You want to keep your object stationary, correct? So you don't even need the coefficient of kinetic friction at all.
  4. Nov 22, 2006 #3
    well, yea, I guess I dont need the coefficient of kinetic friction.
  5. Nov 22, 2006 #4
    hold on, I was mistaken when I said 71.8 was the normal force. 7.5 * g = 73.5.......which is the weight = FN. then, FN * 1 = FN, which is 73.5.

    Thanks for the help moose
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