A 12.1 g CD with a radius of 6.16 cm rotates with an angular speed of 31.1 rad/s. What is its kinetic energy?
C = 3.14 * 2*6.16cm = 38.68cm = 0.387m.
V = 31.1rad/s * (1/6.28)rev/rad * 0.387m/rev = 1.92m/s.
KE=0.5mV^2=0.5 * 0.0121kg * (1.92)^2 = 0.0223J