A phonograph turntable is a uniform disk of radius 15 cm. It has a mass of 600 g

Question

A phonograph turntable is a uniform disk of radius 15 cm. It has a mass of 600 grams and is rotating at 33 revolutions per minute. The phonograph releases an LP record of radius 17 cm and mass 66 grams. Immediately after the record falls, what is the rate of rotation of the record and turntable in revolutions per minute?

A phonograph turntable is a uniform disk of radius 15 cm. It has a mass of 600 grams and is rotating at 33 revolutions per minute. The phonograph releases an LP record of radius 17 cm and mass 66 grams. Immediately after the record falls, what is the rate of rotation of the record and turntable in revolutions per minute?

Explanation / Answer

conservation of angular momenta

Li = Lf

I1w1 = I2w2

I1 = 0.5*0.6*15^2

I2 = 0.5*(0.6*15^2 + 0.066*17^2)

so we get w2 = 28.9 rpm

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