If a force of P $=2$ N causes the $30-$mm$-$diameter shaft to slide along the lubricated bearing with a constant speed of $0\mathrm{.}5$ m$/$s$,$ determine the viscosity of the lubricant and the constant speed of the shaft when P $=8$ N$.$ Assume the lubricant is a Newtonian fluid and the velocity profile between the shaft and the bearing is linear. The gap between the bearing and the shaft is $1$ mm$.$