In a Laboratory Experiment,a Student Brings Up the Rotational Speed

In a laboratory experiment,a student brings up the rotational speed of a flywheel to 30.0 rpm.She then allows it to slow down on its own,and counts 240 revolutions before the apparatus uniformly comes to a stop.The moment of inertia of the flywheel is 0.0850 kg ∙ m².What is the magnitude of the retarding torque on the flywheel?

A) 0.0425 N ∙ m
B) 0.159 N ∙ m
C) 0.0787 N ∙ m
D) 0.000278 N ∙ m
E) 0.0000136 N ∙ m