Posted by Chan on .
hi,need help please.thank.
A car is designed to get its energy from a rotating flywheel (solid disk) with a radius of 2.00 m and a mass of 525 kg. Before a trip, the flywheel is attached to an electric motor, which brings the flywheel's rotational speed up to 4000 rev/min.
(a) Find the kinetic energy stored in the flywheel.
(b) If the flywheel is to supply energy to the car as would a 20.0hp motor, find the length of time the car could run before the flywheel would have to be brought back up to speed.
a) Use the formula E = (1/2) I w^2, where w is the angular speed in rad/s and I is the moment of inertia.
ok this what I try:
first I convert 4000rev/min to rad/s
4000rev/min(2pi/rad/rev)(1.0min/60.0s)
=418.9rad/s
than I plug in E=(1/2)(525kg)(418.9rad/s)=109961.25J the #'s are too big.
(b) Time = (Full speed energy)/Power
You will have to convert horsepower to Watts when using the formula.
This part I'm not sure how to convert in Watts. Sorry but, I am really confuse.Thank again for your time.

physics 
drwls,
1 Horsepower = 746 Watts
The subject is physics. a "physic" is a laxative.
This is the last time I will answer a question with subject title "physic"