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AQA GCSE Physics Energy calculations

Energy calculations

This page covers the following topics:

When a force acts on an object and causes it to move, work is being done on the object by the force. Work done is the measure of Energy Transfer when a force (F) moves a body through a distance (d).

Work done and energy

When an object is pushed over a distance, the work done on the object needs to be calculated in the same direction as the displacement. For example, in the diagram, the box is being pushed horizontally to the right, that means that the work done needs to be calculated using the force which is exerted horizontally. This is done with the formula W = fscos?.

Energy transferred

When an object is moved by a force a graph can be plotted with the object’s displacement on the x-axis and the force exerted on the object on the y-axis. The amount of work done, or energy transferred, to move the object can be calculated by calculating the area under the graph.

Force-displacement graphs

One Watt of power is equal to one Joule (J) of energy being transferred per second (J/s). Power is calculated using the following equation:

Power

E = mcΒ² represents the idea that mass and energy are interchangeable. Generally this equation is used to work out changes in mass and/ or changes in energy rather than simply converting one to another. Examples of this include alpha decay and nuclear reactions.

Energy and mass

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A box is pushed with a steady force of 5 N over a distance of 3 meters. How much work is done on the box by the force?

AQA GCSE Physics Energy calculations A box is pushed with a steady force of 5 N over a distance of 3 meters. How much work is done on the box by the force?
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If a crane lifts a 500 N weight up by 25 m, how much energy is supplied to the crane to move it? Give your answer in kJ.

AQA GCSE Physics Energy calculations If a crane lifts a 500 N weight up by 25 m, how much energy is supplied to the crane to move it? Give your answer in kJ.
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What is the definition of power?

AQA GCSE Physics Energy calculations What is the definition of power?
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A mobile phone needs 25 kJ of energy to be fully charged. The phone charger has a power rating of 4 W, how long will it take to fully charge the mobile phone?

AQA GCSE Physics Energy calculations A mobile phone needs 25 kJ of energy to be fully charged. The phone charger has a power rating of 4 W, how long will it take to fully charge the mobile phone?
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Two lights are left on for 3 hours. One light has a power rating of 65 W and the other is 80 W. How much energy is transferred by the two lights in the 3 hours? Give your answer in kJ.

AQA GCSE Physics Energy calculations Two lights are left on for 3 hours. One light has a power rating of 65 W and the other is 80 W. How much energy is transferred by the two lights in the 3 hours? Give your answer in kJ.
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