Lag1989 problem №4.23

A cylindrical homogeneous shaft with a mass of m = 80 kg and a radius of R = 4 cm rotates at a frequency of n = 9ob / s. At the moment of time t = 0, the brake pad was pressed against the surface of the shaft with a force F = 30 N. The friction coefficient of the pad on the shaft was 0.31. Find the time it takes the shaft to stop.