For a shoe brake, the equivalent coefficient of friction is equal to (where $$\mu $$ = Actual coefficient of friction and $$\theta $$ = Semi-block angle)

A. $$\frac{{2\mu \sin \theta }}{{\theta + \sin \theta }}$$

B. $$\frac{{\mu \sin \theta }}{{2\theta + \sin 2\theta }}$$

C. $$\frac{{4\mu \sin \theta }}{{\theta + \sin \theta }}$$

D. $$\frac{{4\mu \sin \theta }}{{2\theta + \sin 2\theta }}$$

Answer: Option D