Question about the sign of angular velocity

[fredrogers3]

Homework Statement

The problem is here: It is question #4,
http://faculty.mint.ua.edu/~pleclair/ph125/Exams/Ex3/ph125_s09_exam3.pdf

Homework Equations

See Below

The Attempt at a Solution

I have already gotten the answer and know it is correct:
(2m*vi*d)/(((M,clay)+2m)*R^2)
where m is the mass of the clay
My teacher says that the answer I have written above should have a negative sign in front of it. However, I thought angular speed was defined as the magnitude of angular velocity, meaning it is always positive. Who is correct here?

 

[ehild]

You are right, the angular speed was asked, and it is the magnitude of the angular velocity, positive.
The angular velocity itself is negative.

ehild