Flywheels—rapidly rotating disks—are widely used in industry for storing energy. They are spun up slowly when extra energy is available, then decelerate quickly when needed to supply a boost of energy. A 20-cm-diameter rotor made of advanced materials can spin at 100,000 rpm. What is the speed of a point on the rim of this rotor? Suppose the rotor’s angular velocity decreases by 40% over 30 s as it supplies energy. What is the magnitude of the rotor’s angular acceleration? Assume that the angular acceleration is constant. How many revolutions does the rotor make during these 30 s?