Angular work problem

1. Mar 27, 2005

Punchlinegirl

A 42.0 kg wheel, essentially a thin hoop with radius 0.90 m, is rotating at 250 rpm. It must be brought to a stop in 10 s. How much work must be done to stop it.

I used the equation delta K = 1/2 I w^2_f - 1/2 I w^2_i = W and got - 11676 J, but this is not right. Help?

2. Mar 27, 2005

xanthym

From problem statement:
{Hoop Mass} = (42.0 kg)