Energy loss in a pulley, but cleverer

[helloxkitty]

Homework Statement

A block of mass 7.00×10-1kg is suspended by a string which is wrapped so that it is at a radius of 5.80×10-2m from the center of a pulley. The moment of inertia of the pulley is 4.00×10-3kg*m2. There is friction as the pulley turns. The block starts from rest, and its speed after it has traveled downwards a distance of D=0.830m is 1.611m/s. Calculate the amount of energy dissipated up to that point.

given m, r, I, v, D, find Q (energy lost)

Homework Equations

mgh=U(x)
1/2Iw^2
I/2mv^2

The Attempt at a Solution

-mgh=1/2Iw^2+1/2mv^2+Q
solve for Q, get 8.15 J lost. I'm not really sure why I'm unable to get the right answer...unless 8.15 is supposed to be negative. Any thoughts? Thanks so much =)!

 

[Mindscrape]

Hmm, your method is correct. I got -3.25 as the work done by friction. Show a bit more in depth how exactly you made your calculation.