If a ball is given some initial speed v

_{0}, but no angular speed as it's thrown on a surface with a coefficent of friction [itex]\mu[/itex], how long will it take for the ball to execute "perfect roll" ie. roll without slipping?

I did it through conservation of energy, and got

[tex]t = \frac{v_0}{\mu g}[/tex]

Next, I tried with Newton's laws.

I got

[tex]t = \frac{v_0}{\mu g\left(\frac{mr^2}{I} + 1\right)}[/tex]

I suppose the latter's wrong because I cannot simply assume the ball would only rotate about the center of mass -axis (that's what I did).

How do I take this into account?