Rotational kinetic energy question

[physicsbro]

Homework Statement

A car is designed to get its energy from a rotating flywheel with a radius of 1.90 m and a mass of 487 kg. Before a trip, the flywheel is attached to an electric motor, which brings the flywheel's rotational speed up to 5150 revolutions per minute. Find the kinetic energy stored in the flywheel.If the flywheel is to supply energy to the car as would a 11.3 hp motor, how long could the car run before the flywheel would have to be brought back up to speed?

Homework Equations

KE=(1/2)Iw^2

The Attempt at a Solution

 

[rock.freak667]

Homework Statement

A car is designed to get its energy from a rotating flywheel with a radius of 1.90 m and a mass of 487 kg. Before a trip, the flywheel is attached to an electric motor, which brings the flywheel's rotational speed up to 5150 revolutions per minute. Find the kinetic energy stored in the flywheel.If the flywheel is to supply energy to the car as would a 11.3 hp motor, how long could the car run before the flywheel would have to be brought back up to speed?

Homework Equations

KE=(1/2)Iw^2

The Attempt at a Solution

so the ke of the flywheel is?

 

[physicsbro]

I don't know.

 

[rock.freak667]

I don't know.

$$E_k=\frac{1}{2} I \omega^2$$


do you know ω? Do you know what I is for a flywheel?

 

[tiny-tim]

Welcome to PF!

Hi physicsbro! Welcome to PF!

(have an omega: ω and try using the X² tag just above the Reply box )

… Find the kinetic energy stored in the flywheel.
…
KE=(1/2)Iw^2

You need to learn the moment of inertia of the simple shapes …

see eg http://en.wikipedia.org/wiki/List_of_moments_of_inertia"

 

[physicsbro]

I'm not sure if this is right, but this is what i got for ω. i thought it would be 10300π/60s or 539.3 rad/s. I don't what I is for a flywheel, i want to say (1/2)mr^2.

 

[physicsbro]

I found the KE to be 1.28E+08 J, any hints for the second part of the question?

 

[ideasrule]

What is 11.3 hp in joules per second?

 

[physicsbro]

Thanks, i got it.