How Do You Calculate the Moment of Inertia of a Spinning Disc with Added Mass?

In summary, the conversation discusses a horizontal disc spinning at a certain angular speed and the addition of putty to the disc. The moment of inertia of the disc is calculated and the effect of a constant tangential force on the disc is explored. The rotational energy of the system before and after the putty is added is also calculated and the concept of conservation of angular momentum is mentioned.
  • #1
ems1312
12
0

Homework Statement



A) a horizontal disc of diameter 12.0cm is spinning freely about a vertical axis through its centre at an angular speed of 72 revolutions per minute. a piece of putty of mass 5.0g drops onto and sticks to the disc at a distance of 4.0cm from the centre. The angular speed reduces to 60 revolutions per minute. calculate the moment of inertia of the disc. No external torques are applied to the system during this process.

B) A constant tangential force is now applied to the rim of the disc which brings the disc to rest in 6.0 s. Calculate the magnitude of this force.

C) calculate the rotational energy of the system before and after the putty is added to the disc. comment on your answer.
......................

Homework Equations





The Attempt at a Solution



HELP! GOT TILL SATURDAY TO UNDERSTAND IT!
 
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  • #2
No attempt? No thoughts?

Is anything conserved when the putty sticks to the disk?
 
  • #3
momentum?
 
  • #4
ems1312 said:
momentum?

specifically angular momentum. Can you apply the law of conservation of momentum to find the moment of inertia of the disk?
 

Related to How Do You Calculate the Moment of Inertia of a Spinning Disc with Added Mass?

1. What is the definition of moment of inertia?

The moment of inertia of an object is a measure of its resistance to rotational motion, and is calculated based on the mass distribution of the object and its distance from the axis of rotation.

2. How is the moment of inertia of a disc calculated?

The moment of inertia of a disc can be calculated using the formula I = 1/2 * mr^2, where m is the mass of the disc and r is the radius of the disc.

3. How does the moment of inertia of a disc differ from other shapes?

The moment of inertia of a disc is different from other shapes due to its circular geometry. The mass distribution of a disc is concentrated at its center, resulting in a smaller moment of inertia compared to other shapes with similar mass and size.

4. What is the significance of moment of inertia in physics?

Moment of inertia plays a crucial role in rotational motion and is used to calculate the angular momentum and rotational kinetic energy of an object. It also helps in understanding the stability and motion of objects such as a spinning top or a rotating planet.

5. How can the moment of inertia of a disc be measured experimentally?

The moment of inertia of a disc can be measured experimentally by using a torsion pendulum or a rotating platform. These methods involve measuring the angular acceleration of the disc and using it to calculate the moment of inertia using the formula I = mr^2 * α, where α is the angular acceleration.

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