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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.

    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


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    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


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    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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