Finding tangential acceleration of a rotating disk

[AfronPie]

Homework Statement

Attached.

Homework Equations

Tangenital acceleration=r*alpha

3. The Attempt at a Solution
I thought it was just simply r*alpha=2*20=40 (choice A), but the answer key says choice B. I'm not really sure where I could have went wrong or its possible that there is a mistake in the answer key.

Any insight would be very helpful. Thanks.

 

[BvU]

Stick to answer A. Key's wrong.

 

[CWatters]

I think you are correct..

http://spiff.rit.edu/classes/phys211/lectures/tang/tang_all.html

 

[AfronPie]

Stick to answer A. Key's wrong.

Thanks.

 

[scottdave]

I calculate 79 m/s² for the centripetal acceleration (towards the center).