$3\mathrm{.}147$ Bar $B$ slides through a collar in body $C($see Figure

$P3\mathrm{.}147$ and is pinned at $P$ to a second bar $R.$ Both $R$ and $C$

are pinned to the reference frame as shown, and $R$ rotates

with limited motion at constant angular velocity ${}_R^{}$

$=1ra\frac{d}{s}$ counterclockwise. Find the angular velocity of

$C$ when point $P$ is at the top of the circle on which it

travels.