In the equation Eₖ = ½Iω², what does the symbol I represent?

The moment of inertia of the rotating body.

Calculate the rotational kinetic energy when moment of inertia = 45.1 kg m², angular velocity = 84 rad/s.

Rotational kinetic energy = 0.5 × 45.1 × 84 × 84 = 159000 J.

How does increasing the moment of inertia of a flywheel affect its energy storage capacity?

Increasing the moment of inertia increases the energy storage capacity of the flywheel.

How does the energy stored in a flywheel depend on its angular velocity?

The energy stored is proportional to the square of the angular velocity, so greater angular velocity gives greater energy storage.

If the angular velocity of a flywheel is doubled, by what factor does its stored energy change?

The stored energy increases by a factor of four, since energy is proportional to ω².

AQA A-Level Physics 7408

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Engineering Physics

Rotational kinetic energy

3 things to know
Paper 3, section B

Overview

The ½Iω² formula, and the flywheel as an energy store.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

How is rotational kinetic energy calculated, and what does I represent?

Process

How does stored energy depend on angular velocity, and what limits a flywheel's speed?

Numbers

Explain why centripetal stresses in a flywheel increase with rotational speed

Questions from this subtopic

Each one with the model answer underneath.

1
State the formula for the rotational kinetic energy of a rotating body.
Model answer
Eₖ = ½Iω²
2
In the equation Eₖ = ½Iω², what does the symbol I represent?
Model answer
The moment of inertia of the rotating body.
3
Calculate the rotational kinetic energy when moment of inertia = 45.1 kg m², angular velocity = 84 rad/s.
Model answer
Rotational kinetic energy = 0.5 × 45.1 × 84 × 84 = 159000 J.
4
How does increasing the moment of inertia of a flywheel affect its energy storage capacity?
Model answer
Increasing the moment of inertia increases the energy storage capacity of the flywheel.
5
How does the energy stored in a flywheel depend on its angular velocity?
Model answer
The energy stored is proportional to the square of the angular velocity, so greater angular velocity gives greater energy storage.
6
If the angular velocity of a flywheel is doubled, by what factor does its stored energy change?
Model answer
The stored energy increases by a factor of four, since energy is proportional to ω².

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