GCSE Physics resources
AQA GCSE Forces
Stopping distance has a reaction stage and a braking stage. Different factors affect each, so name the stage before explaining a change.
Subsection scope: Stopping distance, reaction-time factors and braking conditions: both courses and tiers. Braking-force/work estimates: Higher. Stopping-distance graph interpretation: Physics only.
Start here
Stopping distance has a reaction stage and a braking stage. Different factors affect each, so name the stage before explaining a change.
Before you revise
Choose an answer from memory. Your result tells you what to watch for in the guide.
Core revision guide
Stopping distance has a reaction stage and a braking stage. Different factors affect each, so name the stage before explaining a change.
Scope: 8463 and 8464 · Foundation and Higher
Thinking distance = speed × reaction time. At 20 m/s and 0.70 s it is 14 m. Tiredness, distraction, drugs and alcohol can lengthen reaction time. Typical reaction times are around 0.2–0.9 s. An electronic reaction test measures elapsed time directly; a ruler-drop test compares catch distance, with repeated trials and a common release procedure. Learning and anticipation are limitations to control.
Scope: 8463 and 8464 · Foundation and Higher
Braking distance starts when braking force acts. Friction does work, reducing kinetic energy and increasing thermal stores in brakes, tyres, road and surroundings. Wet/icy roads, worn tyres or faulty brakes can reduce the available braking force and increase distance. The speed effect is common to both tiers. Higher: with fixed mass and braking force, Fs = ½mv² predicts braking distance proportional to v², so doubling speed requires four times the distance in this model.
Scope: 8463 and 8464 · Foundation and Higher
Stopping distance = thinking + braking distance. Faster speed increases both; longer reaction time only directly increases the thinking stage in an otherwise equal comparison. Physics-only stopping-distance graph tasks and Higher braking-force estimates need their labels. Large deceleration can overheat brakes and increase loss-of-control risk. Road predictions depend on actual conditions rather than a universal memorised distance.
Misconception clinic
Read each belief, say what is wrong with it, then compare your correction.
Tempting idea: 18.75 m.
Use instead: Distance uses multiplication. 15 × 0.80 = 12.
Tempting idea: Longer reaction time only.
Use instead: Reaction time changes thinking distance. Less braking force means more distance to remove kinetic energy.
Retrieval practice
Worked examples
Apply reaction time and thinking distance in the worked reasoning, then try the changed-context questions below.
Scope: 8463 and 8464 · Foundation and Higher
Stopping distance is 49 m.
Exam precision
Do this: Identify the stage each factor changes. State the fixed-force assumption before using energy to compare braking distances.
Independent practice
Write an answer before opening the marking guidance. Then edit the exact phrase or step that would gain the next mark.
Scope: 8463 and 8464 · Foundation and Higher
Original PhysicsUK mark scheme: Point 1 (1 mark): Thinking distance = vt; stopping = thinking + braking. Point 2 (1 mark): Thinking = 18 × 0.75 = 13.5 m; stopping = 13.5 + 24. Point 3 (1 mark): Stopping distance = 37.5 m. Award each distinct point once. Accept equivalent scientifically correct wording. No half marks.
Model answer: Thinking distance = vt; stopping = thinking + braking. Thinking = 18 × 0.75 = 13.5 m; stopping = 13.5 + 24. Stopping distance = 37.5 m.
Acceptable answers: Expected result: Stopping distance = 37.5 m. Accept the unrounded value or a correctly rounded equivalent to two or more significant figures; accept equivalent units if converted correctly. No additional measurement interval is implied.
Marking notes: Method marks remain available after an arithmetic error. Carry an earlier numerical error into a later valid step; award that method point if the unit conversion and physics are correct. A fully correct answer with unit earns all marks unless working is expressly requested.
Scope: 8463 and 8464 · Higher only
Original PhysicsUK mark scheme: Point 1 (1 mark): Kinetic energy ½mv² becomes four times as large. Point 2 (1 mark): Work done by the same force is Fs, so four times the energy needs four times the distance. Award each distinct point once. Accept equivalent scientifically correct wording. No half marks.
Model answer: Doubling speed quadruples kinetic energy. The same braking force must act through four times the distance to remove it.
Useful next steps