Rotation and Linear Motion Help

AI Thread Summary
The discussion revolves around a physics problem involving two connected masses and cylinders, focusing on equilibrium and angular motion. To achieve equilibrium, the mass m2 was calculated to be 6.7 kg. When m2 is removed, the system's angular acceleration and linear speed of m1 must be determined, with emphasis on the connection between the two cylinders and their combined inertia. The teacher clarified that the cylinders should be treated as interconnected for the calculations, which requires consideration of their moment of inertia together. The conversation highlights confusion over the problem's visual representation and the need for a clearer understanding of the system's dynamics.
choi626
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Homework Statement



Two masses, m1 and m2, are connected by light cables to the perimeters of two cylinders of radii, r1 and r2, respectively. The cylinders are rigidly connected to each other but are free to rotate without friction on a common axle. The moment of inertia of the pair of cylinders is I = 45 kgm^2.
r1= 0.5m
r2= 1.5m
m1= 20kg
a) Find the mass of m2 so that the system is in equilibrium
b) the mass is removed and the system released from rest. Determine the angular acceleration, the cable supporting m1, and the linear speed of m1 at the time it has descended 1m.

The Attempt at a Solution


a) T=0
r1F1 - r2F2 = 0
m2= 6.7kg.

b)T=I(alpha)
then how do i go on?
 
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What do you visualize happening to the mass and cylinders after the balancing mass is removed?
 
the wheel rotating in the direction of the heavier mass.

okay umm so my teacher wrote that i have to connect the bodies as well. do i combine the inertias of the two masses

I = I(of m1) + I(of m2).

originally i had (0.5)(20)(9.8)=45(alpha)

but he marked it wrong saying i need to connect the bodies. I don't think i fully understand what he means.
 
w/o a pic, not sure either. I was under the impression that the cylinders were held stationary while the balancing mass was removed and then allowed to accelerate. In other words you had one mass, two cylinders and a brake which was released at t=0
 
Re

yea so i was kinda pissed he didnt put a pic on the test too. but he said that the cylinders are instantaneously stationary when the mass is removed. The smaller cylinder he said can be considered to be inside the big one. The only reason for the two radii is for the inertia equations for the masses.

thanx for replying
 
ok, then the reason they are "connected" is thru the need to conserve momentum. I'm headed for zzzzland, suspect there will be more on this issue in the morning.
 

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