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IGCSEPhysics: Co-ordinated Sciences (Double Award)CIERevision Notes1. Motion, Forces & EnergyEnergy, Work & PowerKinetic Energy

Kinetic Energy (CIE IGCSE Physics: Co-ordinated Sciences (Double Award))

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Kinetic energy

Extended tier only

  • Energy in an object's kinetic store is defined as:

The amount of energy an object has as a result of its mass and speed

  • This means that any object in motion has energy in its kinetic energy store
    • If an object speeds up, energy is transferred to its kinetic store
    • If an object slows down, energy is transferred away from its kinetic store

Kinetic energy of a moving object

1-7-2-kinetic-energy-cie-igcse-23-rn

A moving car has energy in its kinetic store

Kinetic energy equation

  • The amount of energy in an object's kinetic store can be calculated using the equation:

E subscript k space equals space 1 half m v squared

  • Where:
    • E subscript k = kinetic energy, measured in joules (J)
    • m = mass of the object, measured in kilograms (kg)
    • v = speed of the object, measured in metres per second (m/s)

  • The kinetic energy equation demonstrates that if the mass of an object is doubled for a given speed, then its kinetic energy will double
    • This is because kinetic energy is directly proportional to mass
    • E subscript k space proportional to space m
  • If the speed of the object is doubled for a given mass, it will have four times the kinetic energy
    • This is because kinetic energy is directly proportional to velocity squared
    • E subscript k space proportional to space v squared

Worked example

Calculate the kinetic energy stored in a vehicle of mass 1200 kg moving at a speed of 27 m/s.

 

Answer:

Step 1: List the known quantities

  • Mass of the vehicle, m space equals space 1200 space kg 
  • Speed of the vehicle, v space equals space 27 space straight m divided by straight s

Step 2: Write down the equation for kinetic energy

E subscript k space equals space 1 half m v squared

Step 3: Calculate the kinetic energy

E subscript k space equals space 1 half space cross times space 1200 space cross times space open parentheses 27 close parentheses squared

E subscript k space equals space 437 space 400 space straight J

Step 4: Round the final answer to 2 significant figures

E subscript k space equals space 440 space 000 space straight J space open parentheses 2 space straight s. straight f. close parentheses

Examiner Tip

When performing calculations using the kinetic energy equation, always double-check that you have squared the speed. Forgetting to do this is the most common mistake that students make.

You will most likely need to rearrange the kinetic energy equation in your IGCSE Co-ordinated Sciences exam. The kinetic energy equation is one of the more difficult rearrangements at IGCSE, so make sure you are comfortable doing it before your exam!

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    Leander

    Author: Leander

    Expertise: Physics

    Leander graduated with First-class honours in Science and Education from Sheffield Hallam University. She won the prestigious Lord Robert Winston Solomon Lipson Prize in recognition of her dedication to science and teaching excellence. After teaching and tutoring both science and maths students, Leander now brings this passion for helping young people reach their potential to her work at SME.