Torque and Moment of Inertia of a black ring

AI Thread Summary
A black ring on a turntable is subjected to a constant force of 12.5 N, resulting in a calculated angular acceleration of 1.28 rad/s². The net torque is derived from the torques of the pulley, turntable, and ring, totaling 0.8035 N*m. The moment of inertia for the entire system is calculated to be 0.6277 kg*m², with the ring contributing 8.5% of this value. There is confusion regarding whether to include the torque from the turntable in the net torque calculation, as the only applied force is on the pulley. Clarification is needed on the necessity of including additional torques beyond the one directly related to the applied force.
Solemony
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Homework Statement



A black ring is placed concentrically on a turntable and is being pulled by a constant force of 12.5 N and the force is applied at a distance of .01m from the spindle/pulley. It's known that the ring accounts for about 8.50% of the total moment of inertia. Find moment of inertia of turntable in kg*m^2.

Note: And it's being pulled counter clockwise
Note: I have already calculated the alpha to be: 1.28 rad/s^2 (this is from data retrieved from an experiment)

Diameter of pulley :.02m (radius= .01m)
Diameter of turntable: .1m (radius = .05m)
Diameter of inner ring: .05m (radius=.025m)
Diameter of outer ring: .06m (radius= .030m)

2. Homework Equations and attempt at the problem
torque = Radius x Force

torque (pulley): .01m x 12.5N= .125N*m
torque (turntable): .05m x 12.5N = .625N*m
torque (ring): (.030m x 12.5N) - (.025m x 12.5N) = .0535N*m

So Net torque= .125+.625+.0535= .8035 N*m

Total moment of Inertia = .8035N*m/ 1.28 rad/s^2= .6277 kg*m^2

And since the ring accounts for 8.5% of the total moment of inertia I would multiply (.0850)(.6277)= .05335 kg*m^2

Then subtract .05335kg*m^2 from .6277kg*m^2 would give me the moment of inertia for the turntable?

So my question for this problem is that would I need to account the torque calculated for the turntable for the net torque? Because since the pulley/spindle is attached to the turntable and is pulled by the constant force, I would think the torque would have been just the radius of the pulley/spindle multiply by the Force (so net torque would be .125+.0535= .1785N*m instead of .8035N*m). So I wasn't sure about this part and somewhat confused as well... Thanks!

I also provided a picture for reference attached to this thread and also please point out any mistakes I've made as well if there is any calculated mistakes...
 

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Solemony said:
torque (pulley): .01m x 12.5N= .125N*m
torque (turntable): .05m x 12.5N = .625N*m
torque (ring): (.030m x 12.5N) - (.025m x 12.5N) = .0535N*m

So Net torque= .125+.625+.0535= .8035 N*m
I have no idea what you are doing there. Yes, there's an applied torque of .125N*m on the pulley, but what are these other torques? There's not another force of 12.5N applied tangentially to the turntable, is there?
 
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