Law Of Conservation Of Momentum Help

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Discussion Overview

The discussion revolves around the application of the law of conservation of momentum, specifically in the context of a problem involving two flywheels connected by a clutch. Participants seek to understand how this principle applies to their calculations regarding the common speed of rotation and the loss of kinetic energy after the connection. The scope includes theoretical understanding and practical application in a homework context.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Participants discuss the moment of inertia and its role in calculating angular momentum.
  • There are inquiries about the definition of angular momentum in relation to moment of inertia and angular frequency.
  • Some participants emphasize the importance of conservation of angular momentum in solving the problem, noting that kinetic energy is not conserved in this scenario.
  • Questions arise about the implications of the law of conservation not being true, with one participant suggesting it would lead to incorrect values in calculations.
  • Another participant humorously remarks on the broader implications of the conservation law not holding, indicating a fundamental change in the understanding of physics.

Areas of Agreement / Disagreement

Participants generally agree on the application of conservation of angular momentum in the problem, but there is no consensus on the implications of the conservation law not being true, as responses vary from practical concerns about calculations to more philosophical considerations.

Contextual Notes

Some participants mention typos in the problem statement regarding the units of moment of inertia, which may affect clarity in understanding the problem.

StevenBennett
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Homework Statement



A flywheel and shaft have a moment of inertia of 600kg and is rotating at 5 rev/s. Another flywheel and shaft, on the same axis, is suddenly connected by means of a clutch. If this flywheel and shaft has a moment of inertia of 620kg and is initially at rest, calculate:

a) The common speed of rotation after the two are connected

b) The loss in kinetic energy

Answer is attached in document...

But i need to describe the law of conservation of momentum and showing where it is used in this calculation and i need to describe what would the consequence for my calculations were the law of conservation not to be true...

Its for a practice exam paper and i seriously need some help? thanks!
 

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StevenBennett said:

Homework Statement



A flywheel and shaft have a moment of inertia of 600kg and is rotating at 5 rev/s. Another flywheel and shaft, on the same axis, is suddenly connected by means of a clutch. If this flywheel and shaft has a moment of inertia of 620kg and is initially at rest, calculate:

a) The common speed of rotation after the two are connected

b) The loss in kinetic energy

Answer is attached in document...

But i need to describe the law of conservation of momentum and showing where it is used in this calculation and i need to describe what would the consequence for my calculations were the law of conservation not to be true...

Its for a practice exam paper and i seriously need some help? thanks!

Welcome to the PF.

First, there are typos in the units of Moment of Inertia (MOI) where you typed the problem in above. I've bolded the typos -- you can see what is missing by comparing to your attachment.

Second, the attachment does a good job of working through the problem to get to the solutions. Is there some part that you don't understand? What is the definition of the angular momentum of a object in terms of its MOI and it's angular frequency? :smile:
 
berkeman said:
Welcome to the PF.

First, there are typos in the units of Moment of Inertia (MOI) where you typed the problem in above. I've bolded the typos -- you can see what is missing by comparing to your attachment.

Second, the attachment does a good job of working through the problem to get to the solutions. Is there some part that you don't understand? What is the definition of the angular momentum of a object in terms of its MOI and it's angular frequency? :smile:
Heyy yeah i couldn't work out how to square the Kg,

im just trying to work this out:

describe the law of conservation of momentum and showing where it is used in this calculation?

and

to describe what would the consequence for my calculations were the law of conservation not to be true?

But thanks for replying
 
StevenBennett said:
Heyy yeah i couldn't work out how to square the Kg,

im just trying to work this out:

describe the law of conservation of momentum and showing where it is used in this calculation?

and

to describe what would the consequence for my calculations were the law of conservation not to be true?

But thanks for replying

There is an explicit step in that solution where conservation of angular momentum is used. That's why I asked you what the equation is for the angular momentum of a spinning object... :smile:
 
berkeman said:
There is an explicit step in that solution where conservation of angular momentum is used. That's why I asked you what the equation is for the angular momentum of a spinning object... :smile:
The angular moment of a spinning object in this solution is I1W1 + I2W2 = I3W3?
 
StevenBennett said:
The angular moment of a spinning object in this solution is I1W1 + I2W2 = I3W3?

Correct. That line is using the law of conservation of angular momentum. That is how this problem is solved, since kinetic energy is not conserved in this type of collision/rotation-clamping situation. :smile:
 
berkeman said:
Correct. That line is using the law of conservation of angular momentum. That is how this problem is solved, since kinetic energy is not conserved in this type of collision/rotation-clamping situation. :smile:

So what would be the problem if my calculations were the law of conservation not to be true?

Would i just receive a incorrect value?
 
StevenBennett said:
So what would be the problem if my calculations were the law of conservation not to be true?

Would i just receive a incorrect value?

Beats me. That's kind of a weird question. The world wouldn't work anymore... :woot:
 
Yeah that's what's i thought, but cheers for the insight helps a lot!
 

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