IGCSEPhysicsCambridge (CIE)Revision Notes1. Motion, Forces & EnergyEnergy, Work & PowerGravitational Potential Energy

Gravitational Potential Energy (Cambridge (CIE) IGCSE Physics)

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Gravitational potential energy

Extended tier only

  • Energy in an object's gravitational potential energy store is defined as:

The energy an object has due to its height in a gravitational field

  • Work is done against the weight force exerted on the object; therefore, energy is transferred

  • This means that:

    • if an object is lifted up, energy will be transferred to its gravitational potential store 

    • if an object is lowered, energy will be transferred away from its gravitational potential store 

Gravitational potential energy of an object lifted through a gravitational field

1-7-3-gravitational-potential-energy-cie-igcse-23-rn

Energy is transferred to the mass's gravitational store as it is lifted through the gravitational field

Gravitational potential energy equation

  • The change in energy in an object's gravitational potential energy store can be calculated using the equation:

increment E subscript p space equals space m g increment h

  • Where:

    • increment E subscript p = change in gravitational potential energy, measured in joules (J)

    • m = mass, measured in kilograms (kg)

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

    • increment h = change in height, measured in metres (m)

Worked Example

A man climbs a flight of stairs that is, in total, 3.0 m higher than the floor. The man has a mass of 72 kg, and the gravitational field strength on Earth is approximately 9.8 N/kg.

Calculate the energy transferred to the man's gravitational potential energy store.

 

Answer:

Step 1: List the known quantities

  • Mass of the man, m space equals space 72 space kg

  • Gravitational field strength, g space equals space 9.8 space straight N divided by kg

  • Change in height, increment h space equals space 3.0 space straight m 

Step 2: Write down the equation for gravitational potential energy

increment E subscript p space equals space m g increment h

Step 3: Calculate the gravitational potential energy

increment E subscript p space equals space 72 space cross times space 9.8 space cross times space 3.0

increment E subscript p space equals space 2116.8 space straight J

Step 4: Round to an appropriate number of significant figures

  • The input values are to 2 s.f. therefore, the output value must be to 2 s.f.

increment E subscript p space equals space 2100 space straight J space open parentheses 2 space straight s. straight f. close parentheses

Examiner Tips and Tricks

In your IGCSE exam, you will generally be expected to round your answers to an appropriate number of significant figures.

Your answer can only be as accurate as your least accurate input value. Therefore, your final answer should round to the lowest number of significant figures of all your input values.

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