AQA · GCSE · Combined Science

Course version: 8464 · Version from Sept 2018

Energy stores and systems: an object accelerated by a constant force

Q: How do I revise Energy stores and systems: an object accelerated by a constant force for GCSE?

Read the notes on Energy stores and systems: an object accelerated by a constant force, then test yourself without looking. Answering questions and checking what you missed builds recall faster than re-reading.

Q: Is this Energy stores and systems: an object accelerated by a constant force guide aligned to the AQA specification?

Yes. This guide is linked to the Energy stores and systems: an object accelerated by a constant force topic in the AQA GCSE specification.

A constant applied force doing work transfers energy to an object's kinetic store, and potentially its gravitational potential store if it rises.

Study notes

From the checked teaching notes for this specification point.

The idea

For example: A constant push accelerates a trolley along a bench, transferring energy from the pusher's chemical store to the trolley's kinetic store, with some dissipated by friction.

What earns the marks

Identify the constant force doing mechanical work on the object.
State that work done by an applied force transfers energy to the object's kinetic energy store and potentially its gravitational potential store.
Use W = Fs to calculate work done when force and distance are known.
Recognise that a constant resultant force produces constant acceleration via F = ma, and its work equals the change in kinetic energy.
Account for any energy dissipated by friction or air resistance if present.

Common mistakes and how to put them right

Confusing force with energy and giving work done in newtons.
Put it right by using joules for work and newtons for force.
Assuming all work done by an applied force increases kinetic energy when friction is present.
Put it right by subtracting energy dissipated to thermal stores.
Conflating applied force with resultant force.
Put it right by noting that work done by the resultant force equals the change in kinetic energy only.
Using total distance rather than distance moved along the force direction.
Put it right by resolving the force and displacement correctly.

Exam tips

Write the work equation W = Fs before substituting values to make the method clear.
State the direction of motion and force so the sign of work done is unambiguous.
When friction is mentioned, calculate the useful work and the dissipated energy separately.

Try the lesson

The start of the Energy stores and systems: an object accelerated by a constant force lesson, made from checked teaching notes for this specification point.

Have a go first

A toy car is pushed along a straight track by a constant force, so the car speeds up steadily. Which energy store of the car increases because of this acceleration?

Tip: press 1 to 4 to choose

Listen

A constant applied force doing work transfers energy to an object's kinetic store, and potentially its gravitational potential store if it rises. The work done equals force times distance moved along the line of action of the force, W = Fs. If friction is present, some energy is dissipated to the thermal store of the surroundings. Conversely, the work done by the resultant force equals only the change in the kinetic store. If the resultant force is constant, acceleration is constant by Newton's second law, F = ma, so speed increases uniformly. For example, a constant push accelerates a trolley along a bench, transferring energy from the pusher's chemical store to the trolley's kinetic store, with some dissipated by friction. A strong answer earns marks for these points. Identify the constant force doing mechanical work on the object. State that work done by an applied force transfers energy to the object's kinetic energy store and potentially its gravitational potential store. Use W = Fs to calculate work done when force and distance are known. Recognise that a constant resultant force produces constant acceleration via F = ma, and its work equals the change in kinetic energy. A common slip: Confusing force with energy and giving work done in newtons. Instead, using joules for work and newtons for force. Exam tip: Write the work equation W = Fs before substituting values to make the method clear.

See it

A top-down flowchart. The first box, 'Constant force applied to object', points to a second box, 'Work done by force, W = Fs'. This second box branches to three boxes: 'Energy transferred to kinetic store', 'Energy transferred to gravitational potential store if object rises', and 'Energy dissipated to thermal store of surroundings if friction present'. Separately, a box 'Constant resultant force' points to two boxes: 'Constant acceleration via F = ma', which points on to 'Speed increases uniformly', and 'Work done by resultant force equals change in kinetic store'. — It shows how a constant force doing work transfers energy to kinetic and gravitational potential stores, with friction dissipating energy, and how a constant resultant force gives constant acceleration.

Label the diagram

Some boxes have lost their names. Pick the right name for each number.

The diagram again, with 3 boxes numbered instead of named. A top-down flowchart. The first box, 'Constant force applied to object', points to a second box, 'Work done by force, W = Fs'. This second box branches to three boxes: 'Energy transferred to kinetic store', 'Energy transferred to gravitational potential store if object rises', and 'Energy dissipated to thermal store of surroundings if friction present'. Separately, a box 'Constant resultant force' points to two boxes: 'Constant acceleration via F = ma', which points on to 'Speed increases uniformly', and 'Work done by resultant force equals change in kinetic store'.

1Box 1
2Box 2
3Box 3

0 of 3 labelled

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