IB Physics SL

Revision Notes

2.3.1 Kinetic Energy

Kinetic Energy

  • Kinetic energy (Ek) is the 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

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 traveling 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, what is its new kinetic energy?

WE - kinetic energy answer image, 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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