I am supposed to find out only whats wrong with this question, is there a reason

Question

I am supposed to find out only whats wrong with this question, is there a reason why I am unable to solve?

A record player turntable, diameter 40 cm and mass of 1 kg, rotates at a constant 78 revolutions per minute. A record of diameter 26 cm and mass 275 grams is placed on the turntable. (4 Points) W ra a. What is the angular momentum before the record is added? b. What is the combined angular momentum of the turntable and record? V oint Mass mass rotating at a distance r from he axis) lid Disk of radius r with axis of tation at the center) in Rod od of length l rotating about an s through the center)

Explanation / Answer

the moment of inertia of first record player is

I1 = (1/2)*m1*r1^2

= (1/2)*1*0.2^2

= 0.02 kg m^2

The moment of inertia of the second recor player is

I2 = (1/2)*m2*r2^2

= (1/2)*0.275*0.13^2

= 0.002324 kg m^2

convert angualr frequency from rpm to rev/s

w = 78 rev/min

= 78*(2pi/60)

= 8.17 rad/s

beore record plyer added the angualr momentum is

Li = I1 w

= 0.02 ( 8.17)

=0.1634 kg m^2/s

The final angualr momentum

Lf= (I1 + I2) w

L f= (0.2+0.002324)*8.17

= 1.653 kg m^2 /s

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