A grindstone in the shape of a solid disk with diameter 0.520 m and a mass of 50.0 kg is rotating at 850 rev/min . You press an axe against the rim with a normal force of 160 N (see the figure below), and the grindstone comes to rest in 8.00 s.

Find the coefficient of kinetic friction between the axe and the grindstone. There is negligible friction in the bearings. Express your answer to three significant figures.