Energy can be described as being in different ‘stores’. It cannot be created or destroyed but it can be transferred, dissipated or stored in different ways.

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The amount of kinetic energy in a moving object can be calculated using the equation:

This is when:

- kinetic energy (
*E*) is measured in joules (J)_{k} - mass (
*m*) is measured in kilograms (kg) - speed (
*v*) is measured in metres per second (m/s)

An apple of mass 100 g falls from a tree. It reaches a speed of 6 m/s before landing on Isaac’s head. What is the gain of kinetic energy of the apple?

- Question
How much kinetic energy does a 30 kg dog have when it runs at 4 m/s?

The amount of elastic potential energy stored in a stretched spring can be calculated using the equation:

This is when:

- elastic potential energy (
*E*) is measured in joules (J)_{e} - spring constant (
*k*) is measured in newtons per metre (N/m) - extension (
*e*) is measured in metres (m)

Robert stretches a spring with a spring constant of 3 N/m until it is extended by 50 cm. What is the elastic potential energy stored by the spring?

- Question
How much elastic potential energy does a spring store when it is compressed by 0.2 m if it has a spring constant of 5 N/m?

The amount of gravitational potential energy stored by an object at height can be calculated using the equation:

Gravitational potential energy = mass × gravitational field strength × height

This is when:

- gravitational potential energy (
*E*) is measured in joules (J)_{p} - mass (
*m*) is measured in kilograms (kg) - gravitational field strength (
*g*) is measured in newtons per kilogram (N/kg - height (
*h*) is measured in metres (m)

Galileo takes a 5 kg cannonball to the top of the Tower of Pisa for one of his experiments. The tower is 56 m high. How much gravitational potential energy has the cannonball gained? (g = 10 N/kg)

- Question
How much gravitational potential energy does a 500 g book gain when it is lifted up 1.5 m onto a shelf?

For any of these equations you may need to change the subject of the formula.