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AQA A-level Physics Energy calculations

Energy calculations

This page covers the following topics:

1. Energy transferred
2. Force-displacement graphs
3. Power
4. Energy and mass

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

1

A car and a van are both used for pulling a trailer. The car is able to pull the trailer over a distance of 1 km by exerting a force of 900 N at an angle of 10Β°. The van can pull the trailer 1.5 km by exerting a force of 950 N at an angle of 25Β°. The car covers its distance in 45 seconds, and the van covers its distance in 2 minutes. Which vehicle is the most powerful?

A car and a van are both used for pulling a trailer. The car is able to pull the trailer over a distance of 1 km by exerting a force of 900 N at an angle of 10Β°. The van can pull the trailer 1.5 km by exerting a force of 950 N at an angle of 25Β°. The car covers its distance in 45 seconds, and the van covers its distance in 2 minutes. Which vehicle is the most powerful?

2

A lawnmower is being pushed up a hill with an angle of 15Β°. 800 J of energy is used to push the lawnmower up 10 m, calculate the force being exerted on the lawnmower.

A lawnmower is being pushed up a hill with an angle of 15Β°. 800 J of energy is used to push the lawnmower up 10 m, calculate the force being exerted on the lawnmower.

3

James and Emma have identical toy trains. James pushes his train with a force of 13 N at a 50Β° angle to the direction of travel and he supplies the train with 125 J of energy. Emma does 160 J of work to push her train with a force of 14 N at an angle of 30Β°. Calculate who’s train covers the most distance.

James and Emma have identical toy trains. James pushes his train with a force of 13 N at a 50Β° angle to the direction of travel and he supplies the train with 125 J of energy. Emma does 160 J of work to push her train with a force of 14 N at an angle of 30Β°. Calculate who’s train covers the most distance.

4

A fan transfers 1500 J of energy in 30 seconds. What is the power rating of the fan?

A fan transfers 1500 J of energy in 30 seconds. What is the power rating of the fan?

5

A lamp transfers 2460 J of energy in one minute. What is the power rating of the lamp?

A lamp transfers 2460 J of energy in one minute. What is the power rating of the lamp?

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