Belt friction - determining angles

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Homework Help Overview

The problem involves a cable passing around three pulleys that support two blocks, with specific conditions regarding the rotation of the pulleys and coefficients of friction. The objective is to determine the weight range of block A for equilibrium under different scenarios involving pulley D.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster attempts to determine the angles associated with the pulleys, initially using angles from a 30/60/90 triangle but encountering difficulties. They later reconsider the angles for pulleys C and D but remain uncertain about their correctness. Another participant questions whether a couple system or moments should be used for the second part of the problem.

Discussion Status

The discussion has seen some progress, with the original poster indicating they resolved the angle issue for the first part. However, they are now seeking clarification on the approach for the second part of the problem, indicating an ongoing exploration of concepts related to moments and equilibrium.

Contextual Notes

Participants are working with specific constraints regarding the rotation of pulleys and the coefficients of friction, which may influence their reasoning and assumptions about the problem setup.

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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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