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Homework Help: Ladder against wall

  1. May 12, 2010 #1
    1. The problem statement, all variables and given/known data
    A 100-N uniform ladder, 8.0m long, rests against a smooth vertical. The coefficient of static friction between ladder and floor is 0.40. What minimum angle can the ladder make with the floor before it slips?

    3. The attempt at a solution

    Not really sure where to start here. I do know since they told us the ladder is uniform, that i can somehow use the middle of the ladder as something. The sum of torques must be zero if the ladder isn't moving as well. But not quite sure what to do. Any help would be appreciated.
  2. jcsd
  3. May 12, 2010 #2


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    the sum of all forces is also zero if the ladder isn't moving (friction + normal force+gravitional force(=weight))
    so you have two basic conditions:
    1)sum of all forces is zero
    2)as you said , the sum of torques is also zero

    you will calculate the torque(? moment of force) in the point where it touches the wall, and in the point where it touches the floor, and each of those equal zero ( here you will use the middle of ladder) actually it is probably necessary to calculate it around one of this points...

    and at the end some elementary trigonometrics...

    i am sorry, if I used some of the terms incorrectly, english is not my mother tongue, so...
    and I apologize for any physics mistake in the above text, I am just a benevolent student
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