AQA GCSE Physics
AQA GCSE Physics 4.5.6.3 Forces and Braking Exam Questions
Free AQA GCSE Physics exam questions for 4.5.6.3 Forces and Braking, with a mark scheme for every pack. Covers stopping distance, thinking distance, braking distance, reaction time, factors affecting each, braking forces and work done When braking.
4.5.6.3 Forces and Braking exam questions
2 question packs of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About AQA GCSE Physics 4.5.6.3 Forces and Braking
This AQA GCSE Physics section covers how vehicles stop safely. Stopping distance is the sum of thinking distance and braking distance, and each is affected by different factors. You need typical reaction times, a method to measure reaction time, the effect of speed on stopping distance, and how brakes transfer energy by doing work. Higher tier only content includes estimating the forces involved in decelerating road vehicles. It is examined on Paper 2. Examiners test factor questions with clear links to the correct distance, data interpretation and calculations using work done and v^2 minus u^2 = 2 a s.
What you need to know
- Stopping distance Stopping distance = thinking distance + braking distance. For a given braking force, the greater the speed, the greater the stopping distance.
- Reaction time Reaction times vary from person to person, typically 0.2 s to 0.9 s. Reaction time can be measured using a ruler drop test or a computer-based test.
- Factors affecting thinking distance A driver's reaction time is affected by tiredness, drugs, alcohol and distractions. Thinking distance = speed x reaction time, so it is also proportional to speed.
- Factors affecting braking distance Braking distance is affected by adverse road conditions (wet or icy) and poor condition of the vehicle (worn brakes or tyres).
- Braking and work done When a force is applied to the brakes, work done by the friction force between the brakes and the wheel reduces the kinetic energy of the vehicle and the temperature of the brakes increases.
- Speed and braking The greater the speed of a vehicle, the greater the braking force needed to stop it in a certain distance. The greater the braking force, the greater the deceleration. Large decelerations may lead to brakes overheating and/or loss of control.
- Estimating forces (Higher tier only) Estimate the forces involved in the deceleration of road vehicles in typical situations on a public road, for example using v^2 minus u^2 = 2 a s and F = m a.
Common mistakes in 4.5.6.3 Forces and Braking
- Linking tiredness or alcohol to braking distance. They increase reaction time, so they affect thinking distance.
- Linking wet roads or worn tyres to thinking distance. They affect braking distance.
- Saying speed only affects braking distance. Speed increases both thinking and braking distance.
- Saying brakes 'use up' kinetic energy. Work done by friction transfers energy from the kinetic store to the thermal store of the brakes.
- Writing 'reaction time is slower'. Say reaction time is longer (increases).
Try three 4.5.6.3 Forces and Braking exam-style questions
1. A driver travelling at 20 m/s has a reaction time of 0.7 s. Calculate the thinking distance. (2 marks)
Show the mark scheme answer
Thinking distance = speed x reaction time = 20 x 0.7; = 14 m.
2. Give two factors that increase braking distance and explain why each has an effect. (4 marks)
Show the mark scheme answer
Wet or icy road; reduces friction between tyres and road so smaller braking force can be applied without skidding; worn brakes or tyres; reduces the friction (braking) force so deceleration is smaller.
3. Higher tier: A 1200 kg car travelling at 25 m/s stops in a braking distance of 50 m. Calculate the average braking force. (4 marks)
Show the mark scheme answer
Using v^2 minus u^2 = 2 a s: 0 minus 625 = 2 x a x 50; a = minus 6.25 m/s^2 (deceleration 6.25 m/s^2); F = m a = 1200 x 6.25; = 7500 N.
4.5.6.3 Forces and Braking FAQs
What does AQA GCSE Physics 4.5.6.3 Forces and braking cover?
It covers stopping, thinking and braking distances, reaction time and how to measure it, factors affecting each distance, and how braking forces do work on a vehicle.
How do I measure reaction time?
Use a ruler drop test, where a partner drops a ruler and you catch it, then convert the distance fallen into a time, or use a computer-based reaction test. Repeat and take a mean.
Which part of forces and braking is Higher tier only?
Estimating the forces involved in the deceleration of road vehicles is Higher tier only, usually using v^2 minus u^2 = 2 a s with F = m a.
