For the first 20 seconds, the modulus of the angular acceleration is twice the one for the last 40 seconds. (head calculus : it takes twice the time to slow down than it took to reach it's maximum angular velocity.)
A ceiling fan is turned on and reaches an angular speed of 120 rev/min in 20s. It is then turned off and coasts to a stop in an additional 40s. What is the ratio of the avg. angular acceleration for the first 20s to that of the last 40s?