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Homework Help: Sum of torques/friction problem

  1. Nov 6, 2009 #1
    1. The problem statement, all variables and given/known data

    What is the magnitude of the horizontal
    A uniform 7.1 m tall aluminum ladder is leaing against a frictionless vertical wall. The
    ladder has a weight of 227 N. The ladder slips
    when it makes a 52.0◦ angle with the horizontal floor.
    Determine the coefficient of static friction
    between the ladder and the floor

    2. Relevant equations
    sum of torquest ET=0 and newtons second EF=ma

    3. The attempt at a solution

    We did a problem like this in class today but we didnt take the coefficient of friction into account im not sure where to start with this.... I have drawn a diagram.... and since It slips at 52 degrees i believe that is kinetic friction.... rather than the static friction coefficient which i am trying to find out. If i go thought the sum of torques equation i find out that the force force of friction in the x direction should equal the normal force as the ladder pushes against the wall... could some one please help me understand this concept a little better?
  2. jcsd
  3. Nov 7, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    No, all you need to worry about is static friction. The ladder is at the point where it is just about to slip, so static friction is at its maximum.
    Apply all the conditions for equilibrium: ΣF = 0 and ΣT = 0.

    Draw a free body diagram of the ladder.
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