# Physics

A turntable with a moment of inertia of 0.029 kg*m^2 rotates feely at 2.8 rad/s. A circular disk of mass 270 g and diameter 20 cm, and initially not rotating, slips down a spindle and lands on the turntable.

a) Find the new angular speed.
b) What is the change in kinetic energy?

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1. a) Angular momentum about the spindle is conserved.

Iturntable*w1 = (Iturntable+Icd)w2

Solve for the final angular velocity w2.

b) (1/2)*Iturntable*w1^2 - (1/2)(Iturntable + Icd)*w2^2

The formula for the compact disc moment of inertia Icd is:
Icd = (1/2)Mcd*Rcd^2

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posted by drwls

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