Posted by **Anonymous** on Wednesday, November 9, 2011 at 10:27pm.

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?

- physics -
**drwls**, Thursday, November 10, 2011 at 5:07am
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

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