Kinetic Energy Store

Key Stage 3

The car has energy in its kinetic energy store.

The kinetic energy store is the energy store associated with moving objects.

The faster an object moves the more energy it has in its kinetic store.

If two objects are moving at the same speed the one with more mass has more energy in the kinetic store.


The equation for kinetic energy written in words.


The equation for kinetic energy written in symbols.

A 700kg formula one racing car has a top speed of 100m/s. Calculate the kinetic energy of the car to two significant figures.	A cheetah of mass 75kg runs at a speed of 32m/s. Calculate the kinetic energy of the cheetah correct to two significant figures.	A 160g cricket ball is hit at 44m/s. Calculate the kinetic energy of the cricket ball correct to two significant figures.
1. State the known quantities m = 700kg v = 100m/s	1. State the known quantities m = 75kg v = 32m/s	1. State the known quantities m = 160g Convert mass into kilograms. m_{in kilograms} = \(\frac{160}{1000}\) m = 0.16kg v = 32m/s
2. Substitute the numbers into the equation and solve. \(E_k = \frac{1}{2} m v^2\) \(E_k = \frac{1}{2} \times 700 \times 100^2\) \(E_k = \frac{1}{2} \times 700 \times 10,000\) \(E_k = 3,500,000J\)	2. Substitute the numbers into the equation and solve. \(E_k = \frac{1}{2} m v^2\) \(E_k = \frac{1}{2} \times 75 \times 32^2\) \(E_k = \frac{1}{2} \times 75 \times 1024\) \(E_k = 38,400J\) \(E_k \approx 38000J\)	2. Substitute the numbers into the equation and solve. \(E_k = \frac{1}{2} m v^2\) \(E_k = \frac{1}{2} \times m \times v^2\) \(E_k = \frac{1}{2} \times 0.16 \times 44^2\) \(E_k = \frac{1}{2} \times 0.16 \times 1936\) \(E_k = 154.88J\) \(E_k \approx 150J\)

The kinetic energy store is the energy store associated with moving objects.

Any moving object stores kinetic energy.

The kinetic energy store of an object is related to two properties of the object:

The mass of the object - The greater the mass the greater the kinetic energy stored.
The speed or velocity of the object - The greater the speed the greater the kinetic energy stored.

NB: You must memorise this equation!

Kinetic Energy = 0.5 x (Mass) x (Speed)²

\(E_k = \frac{1}{2} m v^2\)

Where:

E_k = Kinetic Energy stored.

m = The mass of the object.

v = The speed or velocity of the object.