Torque problem involving rolling disk stopped by a force

[xregina12]

A potter has a stone disk of radius 0.483 m and mass 101 kg rotating at 71.9 rev/min. The potter stops the wheel in 6.54 seconds by applying a wet towel against the rim with a radially inward force of 103 N. Find the effective coefficient of kinetic friction between the whell and the wet towel.
my work
angular velocity= 71.9 x 2 x pi /60seconds=7.53
alpha =7.53 / 6.54=1.15
Torque=alpha x I = 1.15 x (101) x (.483^2) =27.13 N-M
27.13 = torque = F r sin 90
F =27.13/ (0.483)
F =56.17 Newtons = Frictional force
56.2 = u Fn
u=56.2 / (103) ----> 103 is given as the radially inward force, Fn
u=.545

why is this wrong? does anyone know why? thanks

 

[tiny-tim]

Hi xregina12!

(have an alpha: α and an omega: ω and a mu: µ and a squared: ² )

A potter has a stone disk of radius 0.483 m and mass 101 kg
…
Torque=alpha x I = 1.15 x (101) x (.483^2)

I = mr²/2 …

see http://en.wikipedia.org/wiki/List_of_moments_of_inertia