A cooling fan is turned off when it is running at 860 r e v / m i n . It turns 1
ID: 3900216 • Letter: A
Question
A cooling fan is turned off when it is running at 860rev/min . It turns 1400 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?
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If each of the three rotor helicopter blades is 3.75 m long and has a mass of 135 kg, calculate the moment of inertia of the three rotor blades about the axis of rotation.
How much torque must the motor apply to bring the blades from rest up to a speed of 5.6rev/s in 6.0s ?
Explanation / Answer
angular acceleration is constant
Wave = 860/2 = 430 rev/min
t = 1400/ 430 = 3.2558 min------------>b.
t = 3.2558*60 = 195.34 s
a= 860/3.2558 = -264.143 rev / min^2---------->.a
a=-264.143*(2*3.14)/3600 = -0.46 rad/s^2