# 1.18 Kinetic Energy

## Kinetic Energy

• Kinetic energy (usually written Ek and sometimes KE) is the energy an object has due to its motion (or velocity)
• The faster an object moves, the greater its kinetic energy

• When an object is falling, it is gaining kinetic energy since it is gaining speed
• This energy transferred from the gravitational potential energy it is losing
• An object will maintain this kinetic energy unless its speed changes

• Kinetic energy can be calculated using the following equation:  Kinetic energy (KE): The energy an object has when it is moving

#### Derivation of Kinetic Energy Equation

• A force can make an object accelerate; work is done by the force and energy is transferred to the object
• Using this concept of work done and an equation of motion, the extra work done due to an object's speed can be derived
• The derivation for this equation is shown below: #### Worked example

A body travelling with a speed of 12 m s–1 has kinetic energy 1650 J.

If the speed of the body is increased to 45 m s–1, estimate its new kinetic energy. #### Exam Tip

When using the kinetic energy equation, note that only the speed is squared, not the mass or the ½.

If a question asks about the ‘loss of kinetic energy’, remember not to include a negative sign since energy is a scalar quantity. ### Get unlimited access

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