physics
posted by Anonymous .
A cooling fan is turned off when it is running at 870 rev/min. It turns 1200 revolutions before it comes to a stop.
What was the fan's angular acceleration, assumed constant?
How long did it take the fan to come to a complete stop?

870 rpm = 91.1 rad/s
The average angular velocity during decleration is half that, or
w,av = 45.6 rad/s
The time it takes to stop is
2400*2*pi/45.6 = 165 seconds
If the want the angular acceleration in radians/sec^2, use
alpha = (91.1 rad/s)/165 s