CIE AS Physics (9702) 2019-2021

Revision Notes

6.2.1 Kinetic Energy

Derivation of KE = 1/2mv2

  • Kinetic energy is energy an object has due to its motion (or velocity)
  • 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

Derivation for Kinetic Energy equation

 

Kinetic Energy

  • Kinetic energy is energy an object has due to its motion (or velocity)
    • The faster an object is moving, 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 equation, downloadable AS & A Level Physics revision notes

Equation for Kinetic energy

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

KE: The energy an object has when its moving

Worked example

Worked example - kinetic energy, downloadable AS & A Level Physics revision notes

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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