As shown in the figure, a bob of mass $m$ is tied by a massless string whose other end portion is wound on a flywheel (disc) of radius $r$ and mass $m$. When released from rest the bob starts falling vertically. When it has covered a distance of $h$ the angular speed of the wheel will be

A rigid massless rod of length $3 l$ has two masses attached at each end as shown in the figure. The rod is pivoted at point $P$ on the horizontal axis (see figure). When released from initial horizontal position, its instantaneous angular acceleration will be

A circular disc $D_1$ of mass $M$ and radius $R$ has two identical discs $D_2$ and $D_3$ of the same mass $M$ and radius $R$ attached rigidly at its opposite ends (see figure). The moment of inertia of the system about the axis $OO\text{'}$ passing through the centre of $D_1$, as shown in the figure will be

A solid sphere of $100 \mathrm{kg}$ and radius $10 \mathrm{m}$ moving in a space becomes a circular disc of radius $20 \mathrm{m}$ in one hour. Then the rate of change of moment of inertia in the process is