IB DP Physics: SL复习笔记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 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 what is 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.