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Angular impulse calculations

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A boat's propeller has a rotational inertia of 4.0kgm2. After a constant clockwise torque is applied for 12s, the propeller's angular speed changes from a clockwise 6.0rads to a clockwise 18rads.
What was the torque applied to the propeller?
Answer using a coordinate system where counterclockwise is positive.
  • Your answer should be
  • an integer, like 6
  • a simplified proper fraction, like 3/5
  • a simplified improper fraction, like 7/4
  • a mixed number, like 1 3/4
  • an exact decimal, like 0.75
  • a multiple of pi, like 12 pi or 2/3 pi