1. The problem statement, all variables and given/known data The problem is here: It is question #4, http://faculty.mint.ua.edu/~pleclair/ph125/Exams/Ex3/ph125_s09_exam3.pdf [Broken] 2. Relevant equations See Below 3. 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?