Torque and Moment of Inertia of a black ring

In summary, the problem involves a black ring being pulled by a constant force at a certain distance from a turntable. The ring accounts for 8.50% of the total moment of inertia. Using torque calculations, the moment of inertia of the turntable was found to be 0.6277 kg*m^2. To account for the ring's contribution, 8.50% of the moment of inertia was subtracted from the total, resulting in a moment of inertia of 0.05335 kg*m^2 for the turntable. There may be some confusion regarding the torques calculated for the turntable, as there is a torque applied to the pulley but it is unclear if there is another force applied to the
  • #1
Solemony
6
0

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...
 

Attachments

  • Picture 2.png
    Picture 2.png
    860 bytes · Views: 546
Physics news on Phys.org
  • #2
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?
 

1. What is torque?

Torque is a measure of the force that causes an object to rotate around an axis. It is calculated by multiplying the force applied to an object by the distance from the axis to the point where the force is applied.

2. How is torque related to the moment of inertia?

Torque and moment of inertia are directly related. The moment of inertia is a measure of an object's resistance to changes in its rotation, and torque is the force that causes those changes. The moment of inertia is calculated by multiplying the mass of an object by the square of its distance from the axis of rotation.

3. What is the formula for calculating torque?

The formula for calculating torque is T = F x r, where T is torque, F is the applied force, and r is the distance from the axis of rotation to the point where the force is applied. Torque is typically measured in units of newton-meters (N·m).

4. How is the moment of inertia of a black ring calculated?

The moment of inertia of a black ring can be calculated using the formula I = mR^2, where I is the moment of inertia, m is the mass of the ring, and R is the radius of the ring. This formula assumes that the ring is a thin, hollow cylinder, and the axis of rotation passes through the center of the ring.

5. Why is the moment of inertia important in the study of rotational motion?

The moment of inertia is important in the study of rotational motion because it determines how easily an object can be rotated. Objects with a higher moment of inertia require more torque to be rotated, while objects with a lower moment of inertia require less torque. This concept is crucial in many areas of physics, including the design of machines and vehicles.

Similar threads

  • Introductory Physics Homework Help
Replies
3
Views
856
  • Introductory Physics Homework Help
Replies
13
Views
1K
  • Introductory Physics Homework Help
Replies
8
Views
8K
  • Introductory Physics Homework Help
Replies
7
Views
303
  • Introductory Physics Homework Help
Replies
8
Views
2K
  • Introductory Physics Homework Help
Replies
5
Views
1K
  • Introductory Physics Homework Help
Replies
4
Views
972
  • Introductory Physics Homework Help
Replies
3
Views
2K
  • Introductory Physics Homework Help
Replies
18
Views
6K
  • Introductory Physics Homework Help
Replies
9
Views
1K
Back
Top