The primary disturbing force due to inertia of reciprocating parts of mass \(m\) at radius \(r\) moving with an angular velocity \(\omega\) is given by

(a) \(m \omega^{2} r \sin \theta\)

(b) \(m \omega^{2} r \cos \theta\)

(c) \(m \omega^{2} r \sin \left(\frac{2 \theta}{n}\right)\)

(d) \(m \omega^{2} r \cos \left(\frac{2 \theta}{n}\right)\).