Smallest radius a flywheel can be and still provide enough energy

[mitch_1211]

I am on my second year of study for a bachelor of medical and radiation physics and one of my friends who is studying mechanical engineering ran this question by me, I haven't really had time to go into it in any detail, i thought some of you guys might like to give it a crack:

You set out to design a car that uses the energy stored in a flywheel
consisting of a uniform 100-kg cylinder of radius R. The flywheel
must deliver an average of 2 MJ of mechanical energy per kilometer,
with a maximum angular velocity of 400 rev/s. Find the least value of
R such that the car can travel 300 km without the flywheel having to
be recharged.

Mitch

 

[tiny-tim]

Hi Mitch!

… i thought some of you guys might like to give it a crack …

No, you go first, and then we'll comment.

 

[jschmidt]

I don't believe this forum exists for *doing other people's homework for them*. If your friend is working on the problem, and is running into an error, and wants to post his work thus far, I bet people would be willing to help him find where he's going wrong. If he needs help getting started, if he can explain what he doesn't understand, I bet they would be willing to provide some help that way too, but they aren't going to cheat for him/her.

That said, I can't help because the problem's beyond me. *grin*

 

[timthereaper]

I crunched some numbers and got something like R=1.378 m or something like that. I'm not sure if my process was entirely thorough and I'm not going to post it. I'm just trying to give you something to compare your result with.

As good as your intentions were posting this problem, this isn't like a one-hour cleaners where you can drop off your unsolved problems and pick up the ones that got solved later. There are some really smart people on here, but they want to see a bit of effort first and then they'll teach you how to do the problem.