$9\mathrm{.}23$ The homogeneous horizontal bar $AB$ weighs $200$ N $.$ The homogeneous disk weighs $300$ N $.$ The coefficient of kinetic friction between the disk and the sloping surface is ${}_k=0\mathrm{.}24.$ What is the magnitude of the couple that would need to be applied to the disk to cause it to rotate at a constant rate in the clockwise direction?

$9\mathrm{.}24$ The homogeneous horizontal bar $AB$ weighs $200$ N $.$ The homogeneous disk weighs $300$ N $.$ The coefficient of kinetic friction between the disk and the sloping surface is ${}_k=0\mathrm{.}24.$ What is the magnitude of the couple that would need to be applied to the disk to cause it to rotate at a constant rate in the counterclockwise direction?