1. The problem statement, all variables and given/known data Disk D turns with a constant clockwise angular velocity of 30 . Disk E has a weight of 60 lb and is initially at rest when it is brought into contact with D. Determine the time required for disk E to attain the same angular velocity as disk D. The coefficient of kinetic friction between the two disks is 0.3 . Neglect the weight of bar BC. 2. Relevant equation Summation of forces and moments. 3. The attempt at a solution I am confused with the direction of friction. In my calculations, the friction points to the left because the velocity where the disk meets points to the right; which resulted to a wrong answer. However, the correct free body diagram is shown above.