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.
Examiner 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.
