A helicopter has just landed and as it's engine is turned off, the angular velocity of the rotor blades decreases uniformly from 500 rev/mm to 100 rev/mm in 12.0- s interval.
a) What is the angular acceleration (in rev/s2)?
b) Through how many revolutions does the rotor turn in 12.0-s interval?
c) How long does it take for the rotor to stop?