Forces and motion II

    AQA
    GCSE

    This topic transitions from kinematic description to dynamic analysis, centering on Newton's Second Law as the quantitative link between resultant force, mass, and acceleration. Candidates must apply the principle of conservation of momentum to closed systems involving collisions and explosions, utilizing vector analysis where appropriate. The curriculum further interrogates the mechanics of vehicular motion, requiring a rigorous distinction between thinking and braking distances, and linking these concepts to work done and energy transfer.

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    Objectives
    4
    Exam Tips
    4
    Pitfalls
    4
    Key Terms
    5
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for correct substitution into the equation F = m × a before any rearrangement is attempted
    • Credit responses that explicitly define stopping distance as the sum of thinking distance and braking distance
    • Award 1 mark for stating that the total momentum before a collision equals the total momentum after, provided the system is closed
    • Candidates must link increased reaction time to specific physiological factors (e.g., alcohol, tiredness) rather than external road conditions
    • Award 1 mark for identifying that the force in a collision is equal to the rate of change of momentum (Higher Tier)

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for correct substitution into the equation F = m × a before any rearrangement is attempted
    • Credit responses that explicitly define stopping distance as the sum of thinking distance and braking distance
    • Award 1 mark for stating that the total momentum before a collision equals the total momentum after, provided the system is closed
    • Candidates must link increased reaction time to specific physiological factors (e.g., alcohol, tiredness) rather than external road conditions
    • Award 1 mark for identifying that the force in a collision is equal to the rate of change of momentum (Higher Tier)

    Examiner Tips

    Expert advice for maximising your marks

    • 💡When explaining Newton's Third Law, use the sentence structure: 'Object A exerts force on Object B, so Object B exerts an equal and opposite force on Object A'
    • 💡For 6-mark questions on stopping distance, clearly separate your answer into 'Factors affecting Thinking Distance' (driver) and 'Factors affecting Braking Distance' (car/road)
    • 💡In momentum calculations involving recoil, remember that velocity is a vector; assign a negative sign to the direction of recoil to ensure the total momentum sums to zero
    • 💡Memorize the definition of inertial mass for Higher Tier: it is the ratio of force over acceleration

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Confusing 'braking distance' with 'stopping distance'—candidates often discuss road conditions when asked about thinking distance
    • In Newton's Third Law questions, identifying the reaction force as acting on the same object (e.g., weight and normal contact force) rather than on the interacting object
    • Failing to convert mass from grams to kilograms or speed from km/h to m/s before performing momentum or force calculations
    • Describing the relationship between force and acceleration as linear without specifying 'directly proportional'

    Key Terminology

    Essential terms to know

    Likely Command Words

    How questions on this topic are typically asked

    Calculate
    Explain
    Describe
    Suggest
    Determine
    Compare

    Practical Links

    Related required practicals

    • •{"code":"Required Practical 7","title":"Investigation of Force and Acceleration","relevance":"Investigating the relationship between force, mass, and acceleration using a trolley and light gates or pulley system"}

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