Chapter 9, Problem 59GP

Compact discs. When a compact disc (CD) is playing, the angular speed of the turntable is adjusted so that the laser beam, which reads the digital information encoded in the surface of the disc, maintains a constant tangential speed. The laser begins tracking at the inside of the disc and spirals outward as the disc plays, while the angular speed of the disc varies between 500 rpm and 200 rpm. A certain CD (see Figure 9.34) plays for 74 minutes and has a playing area of outer diameter 12.1 cm (which is also essentially the outside diameter of the disc). (a) What is the tangential speed of the laser beam? (b) What is the diameter of the inside of the playing area of this CD? (c) What is the angular acceleration of the CD while it is playing, assuming it to be constant?

Figure 9.34 Problem 59.