A 0.75kg disk has a radius of 0.20m. H is initially with an angular velocity of
ID: 1549010 • Letter: A
Question
A 0.75kg disk has a radius of 0.20m. H is initially with an angular velocity of 5 rad/s about the same axis of rotation described by the figure in question #2. A second disk (mass = 0.50kg, radius = 0.30m) is placed directly above the first disk and is dropped on the first disk and the system reaches equilibrium. The disks are rough (mu_k = 0.20). a) the initial angular momentum of the system b) the final angular velocity of the system c) If the system reaches equilibrium in 0.20s, determine the average torque on the dropped disk. d) what caused this torque?Explanation / Answer
(A) initial angular momentum of system = I w
= (0.75 x 0.20^2 / 2) ( 5)
= 0.075 kg m^2 / s
(B) angular momentum will be conserved.
hence final angular momentum = 0.075 kg m^2
(0.75 x 0.20^2 / 2 + 0.50 x 0.30^2 / 2) w = 0.075
w = 2 rad/s
(C) change in angular momentum for any disc = torque x time
(0.75 x 0.20^2 / 2) ( 5 - 2) = torque x 0.20
torque = 0.225 N m
(D) friction cause this torque.
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