# Homework Help: Question in momentum of inertia

1. Jun 25, 2012

### manal950

http://store2.up-00.com/June12/ScF29742.jpg [Broken]

and I don't understand what mean by Speeeeed varies from above and below ? b]

Last edited by a moderator: May 6, 2017
2. Jun 26, 2012

### manal950

where are you ?

3. Jun 26, 2012

### Staff: Mentor

I believe it means that the flywheel smoothing is not perfect, it does not iron the speed out to be a perfectly constant 430 RPM. Rather, it smooths it out so that as the flywheel rotates, its instantaneous angular velocity during every revolution varies from a few % less than [what equates to] 430 RPM to the same few % faster than [what would equate to] 430 RPM.

430 RPM is the average (or mean) rotational speed.

4. Jun 26, 2012

### manal950

see the teacher said

N1 = 430 + ( 0.02 X 430 ) = 438.6 rpm
N2 = 430 - (0.02 X 430 ) = 421.4 rpm

How is that please tell me

5. Jun 26, 2012

### Staff: Mentor

0.02 is 2% and I think I explained the rest in post #2

6. Jun 26, 2012

### manal950

I know this 430 + ( 0.02)

but why then multiply in 430 ??

7. Jun 26, 2012

### Staff: Mentor

That is how you calculate percent.

1% of 100 kilograms is 0.01 * 100kg = 1kg.

Does that make sense now?

8. Jun 26, 2012