Edexcel International A Level Physics

Revision Notes

1.18 Kinetic Energy

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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:

2-18-kinetic-energy-equation_edexcel-al-physics-rn

Kinetic energy diagram, downloadable AS & A Level Physics revision notes

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:

Derivation of KE = 1_2mv2, downloadable AS & A Level Physics revision notes

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.

2-18-kinetic-energy-calculation_edexcel-al-physics-rn

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.

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