$1)$ An object with an initial angular velocity of $6$rad$/$s undergoes a constant angular deceleration of $5$rad$/$s$2.$ Calculate the angular displacement after $5$s$.\mathrm{}$

$2)$A fan blade rotates with an angular velocity of $10$rad$/$s$.$ If the blade's length is $6$m calculate the linear displacement at the tip of the blade in $20$ s$.$