# Rotational kinetic energy of a flywheel

• mfm578
In summary, the conversation discusses the design of a car that gets its energy from a rotating flywheel and the calculation of the kinetic energy stored in the flywheel. The flywheel has a radius of 1.12 m and a mass of 736 kg, and its rotational speed is increased to 7270 rev/min before a trip. However, the calculated kinetic energy is incorrect and further assistance is needed. The second part of the conversation considers the possibility that the flywheel is modeled as a disk instead of a hoop, and a different formula for calculating the moment of inertia is suggested. The question is then asked how long the car could run with the flywheel supplying energy equivalent to an 11.8 hp motor before it needs
mfm578

## Homework Statement

A car is designed to get its energy from a rotating flywheel with a radius of 1.12 m and
a mass of 736 kg. Before a trip, the flywheel is attached to an electric motor, which
brings the flywheel’s rotational speed up to 7270 rev/min.
Find the kinetic energy stored in the fly-wheel.

## Homework Equations

KE = 0.5*Inertia*w^2
Inertia = m*r^2

## The Attempt at a Solution

KE equation: 0.5*(761.314)^2*(736 kg)*(1.12m)^2 = 267554029.7

PART 2, I don't think I can do this without a correct answer from part 1

If the flywheel is to supply energy to the car as would a 11.8 hp motor, how long could the
car run before the flywheel would have to be brought back up to speed?

Is it possible the flywheel is modeled as a disk rather than a hoop, in which case

I = .5MR^2, not I = MR^2 ?

Yes, try!

ehild

## 1. What is rotational kinetic energy?

Rotational kinetic energy is the energy possessed by a rotating object. In the case of a flywheel, it is the energy that allows it to maintain its rotational motion.

## 2. How is rotational kinetic energy calculated?

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

## 3. What factors affect the rotational kinetic energy of a flywheel?

The rotational kinetic energy of a flywheel is affected by its mass, moment of inertia, and angular velocity. The more mass a flywheel has, the more kinetic energy it will possess. Similarly, the larger the moment of inertia, the more energy it will have. Lastly, a higher angular velocity will result in a greater amount of kinetic energy.

## 4. How is rotational kinetic energy important in flywheels?

Flywheels are often used to store rotational kinetic energy, which can then be converted into other forms of energy such as electricity. This makes them important in applications such as energy storage systems and mechanical devices.

## 5. Can the rotational kinetic energy of a flywheel be increased?

Yes, the rotational kinetic energy of a flywheel can be increased by increasing its mass, moment of inertia, or angular velocity. However, there are limits to how much energy a flywheel can store, as it can only rotate so fast before it becomes unstable and breaks apart.

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