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

AI Thread Summary
To calculate the moment of inertia of a spinning disc with added mass, the conservation of angular momentum is key, as no external torques are applied. The initial angular speed is 72 RPM, which decreases to 60 RPM after the putty sticks to the disc. The moment of inertia can be determined using the formula I_initial * ω_initial = I_final * ω_final. Additionally, a tangential force is applied to bring the disc to rest in 6 seconds, which requires calculating the force using the disc's deceleration. The rotational energy before and after the putty is added can also be computed to analyze the energy changes in the system.
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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.
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Homework Equations





The Attempt at a Solution



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

Is anything conserved when the putty sticks to the disk?
 
momentum?
 
ems1312 said:
momentum?

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

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