Stopping Distance

Stopping Distance is a GCSE physics game about the space a vehicle needs to come to rest. A round has ten questions. You sort road factors, calculate thinking distance or braking distance and combine them to find stopping distance. The question types appear in a different order each round. Later questions use harder numbers and work-energy ideas.

Choose one of four answers. Every answer shows its unit, and the game explains the method after you answer. A correct answer scores 10 points. In a standard round, you can earn 5 extra points by answering within 15 seconds. The clock only removes the bonus when it reaches zero, so you can still answer for 10 points.

Choose Challenge start to begin with more demanding questions. In this mode, an unanswered question closes when its 15-second clock ends. Switch on Practice mode for a ten-question round without a clock. Number keys 1 to 4 choose an answer, and Enter moves to the next question.

Stopping distance is the whole distance a vehicle covers between the driver noticing a hazard and the vehicle stopping. It has two parts: thinking distance and braking distance. Thinking distance happens while the driver reacts. Braking distance happens after the brakes start slowing the vehicle. Add the two distances to find the total.

During the driver's reaction time, the vehicle keeps moving at its current speed. Thinking distance = speed × reaction time. Use metres per second (m/s) and seconds (s) to get an answer in metres (m). For example, at 18 m/s with a reaction time of 0.5 s, the thinking distance is 9 m. If a speed is in kilometres per hour (km/h), divide by 3.6 before using it. The reaction times in this game stay between 0.2 s and 0.9 s.

A higher speed increases both thinking distance and braking distance. With the same reaction time, doubling speed doubles thinking distance. Braking distance grows more quickly. When the braking force and vehicle mass stay the same, the brakes must remove the vehicle's kinetic energy. The energy removed is work done by the brakes: force × distance = ½ × mass × speed². This means twice the speed gives four times the braking distance. A car at 40 m/s needs four times the braking distance it needed at 20 m/s, if the other conditions stay the same.

Road and vehicle conditions can change how well the brakes slow a car. A wet or icy road gives the tyres less grip. Worn tyres or brakes can also increase braking distance. More mass means more kinetic energy to remove at the same speed, so braking distance can rise if the braking force stays the same. Tiredness, alcohol, drugs or a phone distraction can slow a driver's response. These raise thinking distance. They do not make the brakes work differently.

These ideas connect to forces and energy. You can use the physics equation sheet to check the equations your exam board provides.

AQA Physics (8463) covers stopping distance, reaction time and braking in sections 4.5.6.3.1 to 4.5.6.3.4. AQA Combined Science (8464) covers them in 6.5.4.3.1 to 6.5.4.3.4. See the AQA Physics specification and the AQA Combined Science specification.

Edexcel Physics (1PH0) and Combined Science (1SC0) cover reaction time, factors and stopping distance in points 2.27 to 2.31. Point 2.33P adds the squared-speed braking calculation for Physics only. Check the Edexcel Physics specification and Edexcel Combined Science specification.

OCR Gateway Physics A (J249) covers reaction time and stopping-distance factors in P8.1d to P8.1e. Its P8.1f stopping estimates and P8.1h force estimates are Higher tier outcomes. OCR Twenty First Century Physics B (J259) covers these ideas in P4.3 outcomes 14 to 17; outcome 17 is separate-science content. Read the OCR J249 specification and the OCR J259 specification. The work-energy questions here are marked as a Higher challenge.

• Read the question first. It may ask for thinking distance, braking distance or the whole stopping distance.
• For thinking distance, convert the speed to m/s, then multiply by reaction time. Do not add speed and time.
• For stopping distance, add thinking distance and braking distance. If the total and one part are given, subtract to find the missing part.
• When speed doubles, braking distance becomes four times longer under the same conditions. It does not just double.
• In a work-energy question, square the speed before multiplying by half the mass. Divide by force to get distance, or divide by distance to get force.
• Check the unit at the end. A distance is in metres and a braking force is in newtons.

Pause after each answer and name the step that matters: convert, multiply, add, subtract or square the speed. Explaining that choice can catch a mistake before it reaches the final answer.