A hollow cylinder (radius $R$) is rolling against the wall at angular speed $\omega$. The coefficient of friction between the cylinder and the wall(ground) is $\mu$. After how many rotations the cylinder will stop rotating?
So I figured I need to find the time taken for cylinder to stop moving, and that would be $$ \beta=-\omega/t => t = -\omega/\beta $$ Where $\beta$ is angular acceleration, which is known from torques: $$ 2*F_f*R = I*\beta $$ That's where I got stuck... How do I know the friction? I'm familiar with such equation: $$ F_f = \mu*F_n $$ How do I find the normal force? Does it have anything to do with centripetal force?