Meriam, Kraige & Bolton — Plane Kinetics of Rigid Bodies: Problem 6_185

6/185 The compound pendulum is composed of a uniform slender rod of length $l$ and mass $2m$ to which is fastened a uniform disk of diameter $l/2$ and mass $m$. The body pivots freely about a horizontal axis through $O$. If the pendulum has a clockwise angular velocity of 3 rad/s when $\theta = 0$ at time $t = 0$, determine the time $t$ at which the pendulum passes the position $\theta = 90^\circ$. The pendulum length $l = 0.8 \text{ m}$.