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Homework Help: Belt friction - determining angles

  1. Nov 9, 2008 #1
    1. The problem statement, all variables and given/known data
    A cable passes around three 2-in-radius pulleys and supports 2 blocks as shown. Pulleys C and E are locked to prevent rotatoin, and the coefficient of friction between the cable adn the pulleys are static = .20 and kinetic = .15. Determine the range of value of the weight of black A for which equilibrium is maintained (a) if pully D is locked, (b) if pully di is free to rotate.


    2. Relevant equations

    ln(T2/T1) = static * angle

    3. The attempt at a solution

    The main problem i'm having is determining the angles to be used. I can see it's a 30/60/90 triangle. So i tried using pi/3 for the D and pi/6 for C, and that didn't work.

    Then i used pi/3 still for D and changed pi/6 to 2*pi/3. And that didn't work. If anyone could help me with just the angles that'd be much appreciated. I think i have everything after that down. Thanks for all the help :D
  2. jcsd
  3. Nov 9, 2008 #2
    Last edited by a moderator: May 3, 2017
  4. Nov 9, 2008 #3
    nvm i figured it out :D
  5. Nov 9, 2008 #4
    actually...now that i'm trying to figure out the 2nd part....i can't get it...do i have to use a couple system at D or something of that sort? use moments? or am i over thinking it? thanks once again for any help :D
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