How Does a Glass Fibre Flywheel Store Kinetic Energy in Buses?

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Homework Help Overview

The discussion revolves around a problem involving a glass fibre flywheel designed to store kinetic energy from buses during braking. The context includes calculations related to the maximum kinetic energy, moment of inertia, radius, and mass of the flywheel, as well as determining the mean frictional torque during a stop.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Problem interpretation, Assumption checking

Approaches and Questions Raised

  • Participants explore the relationship between the kinetic energy of the bus and the energy stored in the flywheel, questioning how to apply given data and equations. There are discussions on unit conversions and the implications of different units on calculations. Some participants express confusion about the order of calculations required for different parts of the problem.

Discussion Status

Participants have engaged in clarifying the kinetic energy concepts and unit conversions. Some have successfully calculated parts of the problem, while others are still grappling with the equations needed for subsequent sections. There is an ongoing exploration of how to approach the final part regarding mean frictional torque, with hints provided about using changes in kinetic energy and angular motion equations.

Contextual Notes

Participants note the importance of using consistent SI units for mass and speed to ensure accurate kinetic energy calculations. There is also mention of specific constraints in the problem, such as the requirement to answer sections in a given order and the implications of energy loss during the two-minute stop.

  • #31
Katy96 said:
2Pi/60?

A poor guess. It's ##2\pi##. You could always have googled that!
 
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  • #32
Katy96 said:
so how do I change 48km/h into m/s? never mind I got it now!
Is editing a response as you type it a lost skill?

I see this so often it's ridiculous !
 
  • #33
PeroK said:
A poor guess. It's ##2\pi##. You could always have googled that!
okay well do I just divide by 2pi? because I thought you would do 16000X2pi/60
 
  • #34
Katy96 said:
okay well do I just divide by 2pi? because I thought you would do 16000X2pi/60

I see what you did. There are ##2\pi## radians in a revolution, so yes it's ##2\pi /60## to convert from revs per minute to radians per second.
 
  • #35
PeroK said:
I see what you did. There are ##2\pi## radians in a revolution, so yes it's ##2\pi /60## to convert from revs per minute to radians per second.
when I did that I got the right answer so in part c do I use vmax=rωmax or do I use I=0.606mr2
 
  • #36
Katy96 said:
when I did that I got the right answer so in part c do I use vmax=rωmax or do I use I=0.606mr2

Does that give the right answer?

I'm going offline now. Good luck with the rest of it.
 
  • #37
PeroK said:
Does that give the right answer?

I'm going offline now. Good luck with the rest of it.
thanks.
 
  • #38
Its just part e I'm struggling on now
 
  • #39
Katy96 said:
e) Determine also the

Katy96 said:
Its just part e I'm struggling on now
Yes. It is quite the conundrum.
 
  • #40
jbriggs444 said:
Yes. It is quite the conundrum.
sorry it meant to say Determine also the mean frictional torque causing the slowing down in the two minute stop.
 
  • #41
You know how much energy it had at the beginning of the two minute stop. You have already used that to calculate its angular velocity at that time.

The question tells you what fraction of the starting energy it has at the end of the two minute stop. How much energy is that? How fast does that mean that it must be rotating at the end of the two minutes?
 
  • #42
this is what I know, i need to use the change in the KE to find the final angular speed, and hence the angular deceleration, using the equations of angular motion and torque Important to show answer is negative, as result of deceleration
The force providing the centripetal acceleration acts towards the axis so cannot have a torque about it.and flywheel does not stop during the 2 mins.
 
  • #43
Katy96 said:
this is what I know, i need to use the change in the KE to find the final angular speed
Then there is a starting point. What is the change in KE?
 
  • #44
jbriggs444 said:
Then there is a starting point. What is the change in KE?
that's where I get stuck
 
  • #45
The problem statement says that four fifths of the flywheel's energy remains after two minutes.
 

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