$1.(20\%)$ The simple pendulum with a $3$ kg mass is released

$90$

from rest in position $($A$)$ on a vertical plane. As it reaches the bottom position, the cord is wrapped around the smooth fixed point B and continues to swing to position $($B$)$ at $0=20.$ Find

$($a$)$ the velocity of the mass at $($B$),$ and $($b$)$ the magnitude of force R supported by the fixed point B at position $($B$).$