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Calculating KE & Changes in GPE (WJEC GCSE Science (Double Award)): Revision Note

Ann Howell

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WJEC Science (Double Award): PhysicsWJEC Physics

Calculating KE & Changes in GPE

Higher Tier Only

Kinetic Energy

  • Kinetic energy can be calculated using the equation:

k i n e t i c space e n e r g y space equals space fraction numerator m a s s space cross times space v e l o c i t y squared over denominator 2 end fraction

K E space equals space 1 half m v squared

  • Where:

    • KE = kinetic energy in joules (J)

    • m = mass of the object in kilograms (kg)

    • v = speed of the object in metres per second (m/s)

Kinetic Energy of a Moving Car

Kinetic Energy Car, downloadable AS & A Level Physics revision notes

A moving car has kinetic energy because of its mass and speed

Worked Example

Calculate the kinetic energy of 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 = 1200 kg

  • Speed of the vehicle, v = 27 m/s

Step 2: Write down the equation for kinetic energy

K E thin space equals space 1 half m v squared

Step 3: Calculate the kinetic energy

K E thin space equals space 1 half space cross times space 1200 space cross times space 27 squared

KE = 437 400 J

Step 4: Round the final answer to 2 significant figures

KE = 440 000 J

Examiner Tips and Tricks

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.

Change in Gravitational Potential Energy

  • The change in gravitational potential energy, PE, of an object can be calculated using the equation:

    change in gravitational potential energy = mass × gravitational field strength × height

PE = mgh

  • Where:

    • PE = change in gravitational potential energy, in joules (J)

    • m = mass, in kilograms (kg)

    • g = gravitational field strength in newtons per kilogram (N / kg)

    • h = change in height metres (m)

Gravitational Potential Energy of a Mass

gpe man, IGCSE & GCSE Physics revision notes

Raising a mass to a height above the ground gives it gravitational potential energy

Worked Example

A man of mass 70 kg climbs a flight of stairs that is 3 m higher than the floor.

Gravitational field strength, g = 10 N/kg.

Calculate the change in the man's gravitational potential energy.

Answer:

Step 1: List the known quantities

  • Mass of the man, m = 70 kg

  • Gravitational field strength, g = 10 N/kg

  • Change in height, Δh = 3 m

Step 2: Write down the equation for gravitational potential energy

PE = mgh

Step 3: Calculate the gravitational potential energy

PE = 70 × 10 × 3

PE = 2100 J

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    Ann Howell

    Author: Ann Howell

    Expertise: Physics Content Creator

    Ann obtained her Maths and Physics degree from the University of Bath before completing her PGCE in Science and Maths teaching. She spent ten years teaching Maths and Physics to wonderful students from all around the world whilst living in China, Ethiopia and Nepal. Now based in beautiful Devon she is thrilled to be creating awesome Physics resources to make Physics more accessible and understandable for all students, no matter their schooling or background.