Belt friction - determining angles

AI Thread Summary
The discussion centers on a physics problem involving a cable and three pulleys, where the goal is to determine the weight range of block A for equilibrium under different conditions. The user struggles with calculating the angles for the pulleys, initially attempting various values without success. After some trial and error, they express uncertainty about how to approach the second part of the problem, questioning whether to use a couple system or moments at pulley D. The conversation highlights the importance of correctly identifying angles and applying the right equations for static and kinetic friction. Ultimately, the user seeks further clarification on the methodology for the second part of the problem.
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Homework Statement


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.

http://img98.imageshack.us/my.php?image=circleproblemit0.jpg

Homework Equations



ln(T2/T1) = static * angle

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
 
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nvm i figured it out :D
 
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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