Law Of Conservation Of Momentum Help

[StevenBennett]

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!

 

[berkeman]

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?

 

[StevenBennett]

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?

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

 

[berkeman]

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...

 

[StevenBennett]

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...

The angular moment of a spinning object in this solution is I1W1 + I2W2 = I3W3?

 

[berkeman]

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.

 

[StevenBennett]

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.

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?

 

[berkeman]

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...

 

[StevenBennett]

Yeah that's what's i thought, but cheers for the insight helps a lot!