PROBLEM $15\mathrm{.}123$

Collar $D$ slides on a fixed vertical rod. Knowing that the disk has a constant angular velocity of $15ra\frac{d}{s}$ clockwise, determine the angular acceleration of bar $BD$ and the acceleration of collar $D$ when $($a$)=0,$ w$.$ d$($b$)=180$

$($c$)$ At $=90,1C=.$ What does cowerpenting ar equal