Mass needed to rotate wheel and axle (rotational motion)

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SUMMARY

The discussion centers on solving a physics problem involving a wheel and axle with a total moment of inertia of 0.002 kg·m², driven by an 800 g mass. The objective is to determine the distance the mass must fall to achieve a rotational speed of 3 revolutions per second. The solution employs the principle of conservation of energy, equating the initial potential energy of the mass to the final kinetic energy of both the falling mass and the rotating axle. The relationship between linear velocity and angular velocity is established using the formula v = ωr.

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  • Knowledge of moment of inertia calculations
  • Ability to convert between linear and angular velocity
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  • Learn about calculating moment of inertia for various shapes
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MinaHany
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I'm sorry for posting another thread but I'm totally lost here..

Homework Statement


A wheel and axle having a totel moment of inertia of 0.002kgm is caused to rotate about a horizontal axis by means of an 800g mass attached to a cord wrapped around the axle.
The radius of the axle is 2cm. Starting from rest, how far must the mass fall to give the wheel a rotational rate of 3rev/s?
 
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Use energy. Spinning the wheel and axle combo will impart a kinetic energy. The falling mass will have kinetic energy. The state of the system before the mass falls relies on its (the mass) potential energy. Since the mass is attached to the axle, you know that the kinetic energy of the spinning axle and the falling mass are somehow tied together. How so? From there, conservation of energy is your answer. You know the rotational speed of the axle in the final state.
 
Thank you sethric..
I wrote that final KE = inital KE
rotational KE + KE of the mass = PE of the mass

and v=wr to get the v of the mass when the w is 3 rev/s

Best thing around here is nobody gives the answer.. everybody gives you the ideas you need to understand to be able to solve the problem.

I understand it now.. Thanks again.
 

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