# Static friction and equilibrium - problem with geometry

Thanks krab

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joc
darn, i got here too late :P i got

$$D/L \leq \mu\sin\theta + \cos\theta$$

but i didn't go any further. should've realised that applying the cosine rule was the next logical step. oof. krab, why do you use $$\pm\mu$$ as the coefficient of $$B_x$$? doesn't friction always act in the same direction in this particular scenario?

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Doc Al
Mentor
Originally posted by krab

$$\cos\phi\pm\mu\sin\phi=D/L$$
Nicely done, krab!

Doc Al
Mentor
Originally posted by joc
doesn't friction always act in the same direction in this particular scenario?
No, it doesn't. At one extreme it acts upward, at the other downward.

joc
ahh yes, thanks doc.