## Physics: Principles with Applications (7th Edition)

$1.36 \times 10^4 J$
The energy required equals the rotor’s final rotational kinetic energy. The final rotational speed is 8750 rpm = 916.3 rad/s. $$KE_{rot}=\frac{1}{2}I \omega^2 \approx 1.36 \times 10^4 J$$