Stopping Distance

    OCR
    GCSE

    Stopping distance is defined as the sum of thinking distance and braking distance, representing the total distance a vehicle covers from the moment a hazard is perceived to a complete halt. Candidates must distinguish between factors affecting reaction time (thinking distance) and those affecting braking force or friction (braking distance). Advanced analysis requires equating the work done by the braking force to the initial kinetic energy of the vehicle, demonstrating that braking distance is proportional to the square of the speed.

    0
    Objectives
    3
    Exam Tips
    4
    Pitfalls
    4
    Key Terms
    4
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for explicitly stating that stopping distance is the sum of thinking distance and braking distance
    • Credit responses that identify thinking distance as proportional to speed ($d \propto v$) while braking distance is proportional to the square of speed ($d \propto v^2$)
    • Award marks for equating work done by the braking force to the kinetic energy lost by the vehicle ($F \times d = \frac{1}{2}mv^2$)
    • Candidates must link specific environmental factors (e.g., icy roads, worn tyres) exclusively to braking distance, not reaction time

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You correctly identified that rain affects stopping distance, but you must specify that it increases *braking* distance due to reduced friction."
    • "Your calculation is correct, but you missed the mark for 'realistic estimate' — reaction times are rarely above 1 second."
    • "Excellent use of the work done equation. To secure the final mark, explicitly state that kinetic energy is transferred to thermal energy in the brakes."
    • "Be careful with the relationship between speed and distance: remember that braking distance depends on speed squared, not just speed."

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for explicitly stating that stopping distance is the sum of thinking distance and braking distance
    • Credit responses that identify thinking distance as proportional to speed ($d \propto v$) while braking distance is proportional to the square of speed ($d \propto v^2$)
    • Award marks for equating work done by the braking force to the kinetic energy lost by the vehicle ($F \times d = \frac{1}{2}mv^2$)
    • Candidates must link specific environmental factors (e.g., icy roads, worn tyres) exclusively to braking distance, not reaction time

    Examiner Tips

    Expert advice for maximising your marks

    • 💡In 6-mark extended response questions, structure your answer with two clear sub-headings: 'Factors affecting Thinking Distance' and 'Factors affecting Braking Distance'
    • 💡When asked to 'Estimate' a reaction time, use the standard range (0.2s – 0.9s); values outside this are often penalized as unrealistic
    • 💡For Higher Tier scaling questions, remember: if speed doubles, thinking distance doubles, but braking distance increases by a factor of 4

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Conflating factors affecting thinking distance (alcohol, fatigue) with those affecting braking distance (road surface, mass)
    • Assuming braking distance increases linearly with speed; failing to recognize the square relationship (doubling speed quadruples braking distance)
    • Stating that 'time' increases stopping distance without specifying whether it is reaction time or braking time
    • Calculating stopping distance by simply adding speed and time values rather than calculating the respective distances first

    Study Guide Available

    Comprehensive revision notes & examples

    Read Study Guide

    Key Terminology

    Essential terms to know

    Differentiation between thinking and braking distance
    Factors affecting reaction time versus braking efficiency
    Work done by brakes transferring kinetic energy to thermal energy
    The squared relationship between speed and braking distance

    Likely Command Words

    How questions on this topic are typically asked

    State
    Explain
    Calculate
    Estimate
    Describe
    Analyse

    Practical Links

    Related required practicals

    • •{"code":"PAG 3","title":"Investigation of reaction time (Ruler Drop Test)","relevance":"Experimental determination of thinking distance components"}

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