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Homework Help: Impossible Question

  1. Dec 10, 2009 #1
    1. The problem statement, all variables and given/known data
    (8 marks)
    A uniform ladder (m = 35kg) leans against a smooth frictionless wall. The foot of the ladder is 3 m from the wall and an 85kg firefighter stands 3m up the ladder as shown. Find the coefficient of friction of the floor.
    http://i49.tinypic.com/ftdo9g.jpg

    2. Relevant equations
    (Angular Newton's Second Law and Linear Newton's First Law)
    Στ=0 and ΣFx=ΣFy=0
    τ = F⊥r

    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Dec 10, 2009 #2

    ideasrule

    User Avatar
    Homework Helper

    Draw a free-body diagram of the ladder, being sure to include all forces. Then write out Newton's second law for both the horizontal and the vertical directions. For torque, choose a point and write out the rotational analogue of Newton's second law about that point.
     
  4. Dec 10, 2009 #3
    i've tried that, and it gets so complicated and there are so many unknown variables that I get lost every single time. this was actually on my test and i got 0.
     
  5. Dec 10, 2009 #4

    itr

    User Avatar

    ladder is 3m from wall...it connects with the wall 4m high....so get the angle which is tan^-1 of 4/3.....which is 53.1

    then tan53.1=2umg/mg.....which is equal to 2u..
    tan53.1/2=coefficient friction=.67

    i think thats how you do it
     
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