A flywheel of moment of inertia I = 4.0 kg m^2 is rotating at an initial angular speed of 30 rad/s. A constant frictional torque of 12 N m is applied. How long does it take for the flywheel to come to rest?
Answer and explanation
Correct answer: A. 10.0 seconds
- Step 1: Angular acceleration: alpha = tau / I = -12 / 4.0 = -3.0 rad/s^2. Step 2. Angular kinematics: omega_f = omega_i + alpha t. Step 3. 0 = 30 + (-3.0) t => 3.0 t = 30 => t = 10.0 seconds. Answer: 10.0 seconds. Why not the others: 2.5 s divides 30 by 12; 5.0 s uses double the deceleration.
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