Rotational kinetic energy question

In summary: W. So the flywheel would last about 4 hours and 15 minutes.In summary, the car's flywheel has a radius of 1.90 m and a mass of 487 kg. Its rotational speed is increased to 5150 revolutions per minute by an electric motor before a trip. The kinetic energy stored in the flywheel is 1.28E+08 J. If the flywheel is to supply energy to the car as a 11.3 hp motor, it could run for approximately 4 hours and 15 minutes before the flywheel would need to be brought back up to speed.
  • #1
physicsbro
10
0

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

 
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  • #2
physicsbro said:

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?
 
  • #3
I don't know.
 
  • #4
physicsbro said:
I don't know.

[tex]E_k=\frac{1}{2} I \omega^2[/tex]


do you know ω? Do you know what I is for a flywheel?
 
  • #5
Welcome to PF!

Hi physicsbro! Welcome to PF! :smile:

(have an omega: ω and try using the X2 tag just above the Reply box :wink:)
physicsbro said:
… 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" [Broken] :wink:
 
Last edited by a moderator:
  • #6
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.
 
  • #7
I found the KE to be 1.28E+08 J, any hints for the second part of the question?
 
  • #8
What is 11.3 hp in joules per second?
 
  • #9
Thanks, i got it.
 

1. What is rotational kinetic energy?

Rotational kinetic energy is the energy an object possesses due to its rotational motion. It is directly related to an object's moment of inertia and angular velocity.

2. How do you calculate rotational kinetic energy?

The formula for calculating rotational kinetic energy is E = 1/2 * I * ω², where E is the kinetic energy, I is the moment of inertia, and ω is the angular velocity of the object.

3. What is the difference between rotational kinetic energy and linear kinetic energy?

Rotational kinetic energy is the energy associated with an object's rotational motion, while linear kinetic energy is the energy associated with an object's linear motion. They are calculated using different formulas and are measured in different units.

4. How does rotational kinetic energy relate to work and power?

Rotational kinetic energy is closely related to work and power. Work is the transfer of energy, and when a force is applied to an object to make it rotate, work is done on the object, increasing its rotational kinetic energy. Power is the rate at which work is done, so the higher the power, the faster the object's rotational kinetic energy will increase.

5. What are some real-life examples of rotational kinetic energy?

Some examples of rotational kinetic energy in everyday life include a spinning top, a swinging pendulum, a rolling wheel, and a spinning ceiling fan. In nature, rotational kinetic energy can be seen in the rotation of planets and stars, and in the spinning motion of atoms and molecules.

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