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

Question

A ring (2 kg, r = 2 m) rotates in a CW direction with initial angular velocity 20 s-1. A disk (4 kg, r = 2 m) rotates in a CCW direction with initial angular velocity 60 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 Li of the ring+disk system?
kg m2 s-1
Tries 0/3

What is the final angular velocity ?f of the ring+disk system?
s-1
Tries 0/3

Explanation / Answer

angular momentum = Iw w for ring = -20 rad/sec w for disc = 60rad/sec I for ring = mr2= 2*4=8 kgm2 I for disc = mr2/2 = 4*4/2 = 8 kgm2 initial andular momentum I1w1+I2w2 = -8*20 + 8*60 = 640 kg m2 s-1 ANS (I) apply conservation of angular momentum: finally the disks will be rotating with the same angular velocity as their radii are same.. so, let the final angular velocity be x. 640=8*x+8*x x=640/16 x=40 rad/sec ANS (II)

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