A ring (4 kg, r = 2 m) rotates in a CW direction with initial angular velocity 1

Question

A ring (4 kg, r = 2 m) rotates in a CW direction with initial angular velocity 10 s-1. A disk (8 kg, r = 2 m) rotates in a CCW direction with initial angular velocity 50 s-1. The ring and disk collide" and eventually rotate together. Assume that positive angular momentum and angular velocity values correspond to rotation in the CCW direction. What is the initial angular momentum L of the ring+disk system? Remember that L (system) L (ring) + L (disk), where L Iw for each obj Submit Answer Incorrect. Tries 1/3 Previous Tries What is the final angular velocity of of the ring+disk system? kg m2 s1 Submit Answer Tries 0/3

Explanation / Answer

moment of inertia of ring I1 = m1*r1^2 = 4*2^2 = 16 kg m^2

angular momentu of ring L1 = I1*w1 = -16*10= -160 kg m^2/s

moment of inertia of disk I2 = (1/2)*m2*r2^2 = (1/2)*8*2^2 = 16 kg m^2

angular momentu of disk = I2*w2= 16*50 = 800 kg m^2/s

total initial angular momentum Li = L1 + L2

Li = I1*w1 + I2*w2

Li = -160 + 800 = 640 kg m^2/s <<<--------ANSWER

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after collision

totla moment of inertia I = (I1+I2)

angular momnetum Lf = (I1+I2)*wf

from conservation of angular momemtum

Lf = Li

(16 + 16)*wf = 640

angular velocity wf = 20 s-1

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