A flywheel with moment of inertia 20 kg m^2 accelerates from rest under a constant torque of 100 N m. What is its angular kinetic energy after 4 seconds?
Answer and explanation
Correct answer: A. 4,000 J
- Step 1: Angular acceleration alpha = tau / I = 100 / 20 = 5.0 rad/s^2. Angular velocity after 4 s is omega = 5.0 4 = 20 rad/s. Step 2. Rotational kinetic energy E = 0.5 I omega^2 = 0.5 20 (20)^2 = 10 400 = 4,000 J. Answer: 4,000 J. Why not the others: Alternatively, work done W = tau theta = 100 (0.5 5 16) = 100 * 40 = 4,000 J.
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