# physics.

posted by .

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.

• physics. -

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. -

I did the same thing, but I can't get the right answer.

• physics. -

• physics. -

But the book says the right answer should be 6.0*10^5rev/min

• physics. -

That is pretty mysterious.

## Similar Questions

1. ### Physics

The moment of inertia of an object depends on the shape of the object, location and orientation of the axis of rotation. For a solid disk, when the disk is rotating about an axis that is perpendicular to the disk and passing through …
2. ### physics

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 …
3. ### phys

A disk rolls down a slope. It rotational axis is its center of mass. It is rotation at a constant angular speed making 34.0 full revolutions in a time interval of 3.30 s. 1)What is the rotational inertia of the disk if its mass is …
4. ### physics

An experimental flywheel, used to store energy and replace an automobile engine, is a solid disk of mass 202.0 kg and radius 0.35 m. (a) What is its rotational inertia?
5. ### Physics

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 …
6. ### physics

A car is designed to get its energy from a rotating flywheel (solid disk) with a radius of 1.00 m and a mass of 600 kg. Before a trip, the flywheel is attached to an electric motor, which brings the flywheel's rotational speed up to …
7. ### physics

A car is designed to get its energy from a rotating flywheel (solid disk) with a radius of 1.00 m and a mass of 600 kg. Before a trip, the flywheel is attached to an electric motor, which brings the flywheel's rotational speed up to …
8. ### pysics

Consider a 6·kg disk with a radius of 0.6·m and rotating about an axis passing through its center. (a) What is its rotational inertia?
9. ### physics

A disk with a rotational inertia of 1.4 kg×m2 and a radius of 0.8 m rotates on a frictionless fixed axis perpendicular to the disk faces and through its center. A force of 5.2 N is applied tangentially to the rim. The angular acceleration …
10. ### physics

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 …

More Similar Questions