Homework Help: physics.

Posted by Disy on Saturday, January 5, 2008 at 7:57pm.

A flywheel is a solid disk that rotates about an axis that is perpendicular to the disk at its center. Rotating flywheels provide a means for storing energy in the form of rotational kinetic energy and are being considered as a possible alternative to batteries in electric cars. The gasoline burned in a 300-mile trip in a typical midsize car produces about 1.2*10^9 J of energy. How fast would a 13-kg flywheel with a radius of 0.30m have to rotate to store this much energy? Give your answer in rev/min.

I need some hints to do this problem. Please help. Thanks.

physics. - Damon, Saturday, January 5, 2008 at 8:26pm
The kinetic energy stored in a rotating object is

(1/2) I w^2

I is the moment of inertia of the disk about an axis perpendicular to the disk at the center, which you can look up (If they want you to derive it reply to me that you need a derivation)
I = (1/2) M R^2 where R is the radius of the flywheel and M is the mass
w is the angular velocity in radians per second
w = 2 pi (revolutions per second)
so set your Joules equal to (1/2) I w^2 and solve for w
then change w from radians per second to revs per minute
revs/min = w in rad/sec * 1 rev/2pi radians * 60 seconds/1 minute
- physics. - Disy, Saturday, January 5, 2008 at 8:35pm
  I did the same thing, but I can't get the right answer.
  My answer is 4.3*10^5 rev/min
physics. - Damon, Saturday, January 5, 2008 at 8:48pm
I agree with your answer
- physics. - Disy, Saturday, January 5, 2008 at 8:51pm
  But the book says the right answer should be 6.0*10^5rev/min
physics. - Damon, Saturday, January 5, 2008 at 8:54pm
That is pretty mysterious.

Answer this Question

Related Questions

Physics - A flywheel is a solid disk that rotates about an axis that is ...
Physics - A solid disk rotates in the horizontal plane at an angular velocity of...
Physics - A solid disk rotates in the horizontal plane at an angular velocity of...
Physics - A large disk of mass M and radius R is spinning like a CD of merry-go-...
physics - A children's merry-go-round in a park consists of a uniform 200kg ...
Physics - A penny is placed at the outer edge of a disk (radius = 0.159 m) that ...
Physics - A penny is placed at the outer edge of a disk (radius = 0.159 m) that ...
Physics - A solid cylindrical disk has a radius of 0.18 m. It is mounted to an ...
physics - A solid cylindrical disk has a radius of 0.17 m. It is mounted to an ...
physics - A 1.6 kg disk with radius 0.63 m is rotating freely at 55 rad/s ...

For Further Reading

First Name:
School Subject:
Answer: