two disks are located on an axle as shown in the figure. The lower disk is initi
ID: 2024225 • Letter: T
Question
two disks are located on an axle as shown in the figure. The lower disk is initially spinning counterclockwise at 50 rad/s, and the upper one is not spinning. The upper disk then falls onto the lower disk, and they stick together.
a) is there a torque on the lower disk ? on the upper disk ?
b) identify a system for which the external torque is zero so that the angular momentum is conserved.
c)what is the initial angular momentum of your system ?
d) what is the final angular momentum of your system ? (express answer in terms of final, the final angular velocity of the two disks).
e) find final.
Explanation / Answer
a) yes there is torque on both disks. Remember T=Iw=Fd. both have the same axis of rotation
b) The external torque is zefo for a system comprimised of both disks
c) only disk one is spinning so L=Iw=1/2 mr^2= (0.5*20*2^2)(50)= 2000
d) Momentum is consereved in the system and now you have to account for the moment of inertia (I) of both the other disk
sum T=Iw
(0.5*20*2^2)w + (0.5*7*1^2)w =0
this one is confusing because it says express in terms of w final so your answer is
43.5wf
e) initial momentum = final momentum
2000= (I total) * w
w=43.5 (previous problem)
w final =45.98
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