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1.5.2States of Matter

Stopping Distance — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 5 parts Lesson 6 of 30 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
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Section 1 of 5Parts of Stopping Distance

Stopping distance has two parts, and each part is affected by different factors.

Stopping distance
  • Stopping distance The total distance travelled from the moment a hazard is seen until the vehicle comes to rest, equal to thinking distance plus braking distance.
Thinking distance
  • Thinking distance The distance travelled during the driver's reaction time, which depends mainly on the speed of the vehicle.
Braking distance
  • Braking distance The distance travelled while the braking force slows the vehicle down to rest.
Reaction time
  • Reaction time The time between seeing a hazard and applying the brakes, which is about 0.25 s on average for a human.

Section 2 of 5Factors Affecting Stopping Distance

Factors Affecting Stopping Distance
Speed
  • Speed A higher speed increases both thinking distance and braking distance, so stopping distance rises quickly with speed.
Driver condition
  • Driver condition Tiredness, distraction and alcohol or drugs lengthen the reaction time, which increases thinking distance.
Vehicle condition
  • Vehicle condition Worn tyres or poor brakes reduce the braking force, which lengthens the braking distance.
Road and mass
  • Road and mass Wet or icy roads and heavier vehicles increase the braking distance, because they reduce the deceleration available.

Section 3 of 5Calculating Stopping Distance

Thinking distance depends on speed, so the speed must be in m/s before it is multiplied by the reaction time.

1
Calculate the thinking distance using thinking distance = speed × reaction time, with the speed in m/s.
2
If the stopping distance is given, find the braking distance by subtracting the thinking distance from it.
3
Add the thinking distance and the braking distance to find the total stopping distance.
4
Check that a faster vehicle gives a larger braking distance for the same braking force.

Section 4 of 5Worked Example

Question

  • A car travels at 20 m/s.
  • The driver's reaction time is 0.5 s and the braking distance is 30 m.
  • Calculate the stopping distance.

  1. Thinking distance = speed × reaction time = 20 × 0.5 = 10 m.
  2. Stopping distance = thinking distance + braking distance = 10 + 30.
  3. Stopping distance = 40 m.

Answer The stopping distance is 40 m.

Section 5 of 5Exam Checklist & Tips

1.5.2 – Key Points for the Exam

  • Stopping distance The total distance a vehicle travels from seeing a hazard until it stops.
  • Thinking distance The distance a vehicle travels during the driver's reaction time.
  • Braking distance The distance a vehicle travels while its brakes are applied and it slows to rest.
  • Reaction time The time between noticing a hazard and beginning to brake.

Common Mistakes

  • Adding the reaction time directly to a distance, without multiplying it by the speed.
  • Confusing thinking distance with braking distance; thinking distance is travelled before the brakes act.
  • Stating that reaction time changes the braking distance; it affects only the thinking distance.
  • Using a speed in mph without converting it into m/s before calculating the thinking distance.

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