Plug in time to find the acceleration

Heres the problem Im working on...

http://img502.imageshack.us/img502/1613/rotut5.jpg [Broken]

Im trying to figure how to plug in time to find the acceleration....

I found the first acceleration of 100mm/s^2......but im not sure how to get the others...

I was using the formula

[tex] a_{t} = r\theta [/tex]

[tex] a_{n} = r\omega^2 [/tex]

 

at time = 0 I was able to do

[tex] a_{t} = r\omega = 9(.200)(.5) = .100 = 100mm/s^2 [/tex]

and that is correct for the first answer....

but for the other times I wasnt sure...

 

ok I figured it out for time at 2...and its the same for each time....its just

[tex] a_{t} = r\alpha = (.200)(.5) = .100 [/tex]

[tex] \omega = \omega_{o} + \alpha(t) [/tex]

[tex] \omega = .5 rad/s[/tex]

[tex] a_{n} = r\omega^2 = (.200)(.5)^2 = .050[/tex]

[tex]A = \sqrt{a_{t}^2+a_{n}^2} = 111.8 mm/s^2[/tex]