$($numbers $21-22)$ A small ring is released from rest halfway up from the bottom of a half$-$pipe of radius $4$ m $.$ The ring rolls without slipping. At the Iow point:

$21.$ The speed of the ring's center is:

a$)4\mathrm{.}47\frac{m}{s}$

b$)4\mathrm{.}87\frac{m}{s}$

perpendicuar roll w$/$o slipping $mgy=\frac{1}{2}m{v}_f^2$ to motion ${}_{NGF}=0$Ln