Under active development is the storage of energy in high-speed rotating disks where friction is effectively eliminated by encasing the rotor in an evacuated enclosure and by using magnetic bearings. For a 10-kg rotor with a radius of gyration of 90 mm rotating initially at 80 000 rev/min, calculate the power P which can be extracted from the rotor by applying a constant 2.10-N∙m retarding torque 

(a) When the torque is first applied 

(b) At the instant when the torque has been applied for 120 seconds.