How Fast Does a Flywheel Spin in a Stopping Hybrid Car?

  • Thread starter Thread starter madmike1
  • Start date Start date
  • Tags Tags
    Flywheel
Click For Summary

Homework Help Overview

The discussion revolves around the physics of energy transfer in a hybrid vehicle using a flywheel during braking, as well as the dynamics of a downhill cart race. The original poster presents two distinct problems: one involving the calculation of the flywheel's speed when a car stops and another concerning the maximum speed and timing of a cart race on a slope.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants explore the relationship between kinetic energy and rotational energy, questioning how to apply the conservation of energy principles to the flywheel scenario. There is also discussion about the assumptions made regarding the car's speed in an urban area and its implications for the calculations. In the cart race problem, participants consider the maximum speed attained down the hill and the method for calculating it.

Discussion Status

The discussion is ongoing, with participants sharing their thoughts on the necessary assumptions and calculations. Some guidance has been offered regarding the relationship between kinetic and rotational energy, and there is active questioning about the validity of certain assumptions, such as the speed limit in urban areas and its effect on the calculations.

Contextual Notes

Participants note the importance of the car's speed, particularly the assumption of 30 mph in an urban area, which is not explicitly stated in the original problem. There is also mention of the need to account for the change in kinetic energy as the car decelerates.

madmike1
Messages
4
Reaction score
0
I need a bit of help with a few questions.

In a hybrid vehicle a flywheel is used to capture the energy of the car during braking. If the car has a total mass of 850kg and the flywheel has a mass-moment of inertia equal to 14kgm2 determine the speed of the flywheel when the car stops for traffic lights in an urban area (you may assume 100% efficiency).

and...

A downhill cart race is to start at 10.30 am precisely. The hill has a slope that varies from 1:4 to 1:10 and has a vertical drop of 75m. If the track length is 0.75km (the first 0.5 km being the hill itself) and assuming no energy losses determine
a) the maximum speed attained
b) the time the first cart crosses the finish line

thanks
 
Physics news on Phys.org
Welcome to PF! What have you attempted so far with these questions. You cannot receive any help until you have made some effort yourself.
 
change in kinetic energy of car to rotational energy of flywheel
so would have 0.5MV^2=0.5Iw^2

=> w^2=(M/I)V^2
=> w=7.79V
and then the drop from 30mph to zero needs to be taken into account somehow.

am i right?
 
and then the drop from 30mph to zero needs to be taken into account somehow.
Yes - the change in kinetic energy based on the velocity decreasing from 30 mph to 0 goes into the flywell, which increases it rotational kinetic energy.

BTW, the 30 mph is not mentioned in the OP. This is necessary piece of information in this problem.
 
it mentions that it is in an urban area so i assumed that the speed limit would be 30 therefore the speed of the car would be 30?? i don't know though
 
madmike1 said:
it mentions that it is in an urban area so i assumed that the speed limit would be 30 therefore the speed of the car would be 30?? i don't know though

Yes, if you're in the Uk then the speed limit will be 30mph for the urban area. You can then work out the change in kinetic energy.
 
would the maximum speed attained down the hill be 38.36m/s?
using v=sqrt2gh?
or is velocity not the same as maximum speed?
 


Could anyone confirm if this is correct, including the thread starter?

Thanks
 

Similar threads

How Does a Glass Fibre Flywheel Store Kinetic Energy in Buses?
  • · Replies 44 ·
2
Replies
44
Views
5K
Calculating Flywheel Speed in a Hybrid Vehicle: A Homework Challenge
  • · Replies 3 ·
Replies
3
Views
2K
What is the maximum attainable speed for the car?
  • · Replies 4 ·
Replies
4
Views
2K
Can a Flywheel Efficiently Power a Low-Pollution Car for Long Distances?
  • · Replies 1 ·
Replies
1
Views
6K
Calculating torque required to operate a flywheel
  • · Replies 8 ·
Replies
8
Views
7K
Undergrad How find moment of inertia for car in turn?
  • · Replies 49 ·
2
Replies
49
Views
6K
How Does a Flywheel Prevent a Car from Rolling Over in High-Speed Turns?
  • · Replies 1 ·
Replies
1
Views
9K
Car Crash Analysis: Analyzing Friction & Speed
  • · Replies 9 ·
Replies
9
Views
5K
Auto/Motor Can a 5 HP Gas Motor and a Flywheel Revolutionize City Driving?
  • · Replies 6 ·
Replies
6
Views
4K
Calculating Stopping Time for a Flywheel & Disk Brake System
  • · Replies 10 ·
Replies
10
Views
5K