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 20.0-hp 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.
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"
No problem! I can help you with the conversion from horsepower to Watts.
First, let's convert the horsepower to Watts. One horsepower is equal to 746 Watts. So, to convert 20 horsepower to Watts, you can multiply by the conversion factor:
20 horsepower * 746 Watts/horsepower = 14920 Watts
Now, we can proceed with the calculation for part (b) of your question.
In part (b), you want to find the length of time the car could run before the flywheel would have to be brought back up to speed. To do this, we can use the formula:
Time = (Full speed energy) / Power
We already calculated the kinetic energy stored in the flywheel in part (a) as 109961.25 Joules. The power is given as 14920 Watts.
Now, we can substitute these values into the formula:
Time = (109961.25 J) / (14920 W)
Calculating this division, we find:
Time ≈ 7.38 seconds
Therefore, the car could run for approximately 7.38 seconds before the flywheel would have to be brought back up to speed.
I hope this explanation helps! If you have any more questions, feel free to ask.