Solve this:
Q.15. A rod of mass m and length 2R can rotate about an axis passing through O in vertical plane. A disc of mass m and radius R is hinged to the other end P of the rod and can freely rotate about P. When disc is at lowest point both rod and disc has angular velocity $\omega$. If rod rotates by maximum angle $\theta =60°$ with downward vertical, then find $\omega$ in terms of R and g. (all hinges are smooth)