For a block brake, the equivalent coefficient of friction is equal to:

(a) \(\frac{4 \sin \theta}{2 \theta+\sin 2 \theta} \mu\)

(b) \(\frac{2 \sin \theta}{2 \theta+\sin 2 \theta} \mu\)

(c) \(\frac{4 \sin 2 \theta}{2 \theta+\sin 2 \theta} \mu\)

(d) \(\frac{2 \sin 2 \theta}{2 \theta+\sin 2 \theta} \mu\)