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Fig. 20.1 shows thinking, braking and stopping distances for the same car travelling at different speeds - OCR Gateway - GCSE Physics - Question 20 - 2018 - Paper 1
Question 20
Fig. 20.1 shows thinking, braking and stopping distances for the same car travelling at different speeds. Speed (m/s) 8 16 32 Thinking distance (m) 6 12 24 Brakin... show full transcript
Worked Solution & Example Answer:Fig. 20.1 shows thinking, braking and stopping distances for the same car travelling at different speeds - OCR Gateway - GCSE Physics - Question 20 - 2018 - Paper 1
Step 1
Describe how the thinking distance changes when the speed doubles.
Answer
When the speed doubles, the thinking distance also doubles. For example, at 8 m/s, the thinking distance is 6 meters, and at 16 m/s, it is 12 meters. This consistent doubling of distances demonstrates that thinking distance is directly proportional to speed.
Step 2
Calculate the reaction time of the person driving the car.
Answer
To calculate the reaction time, we use the formula:
ext{Reaction time} = rac{ ext{Thinking distance}}{ ext{Speed}}For instance, using the thinking distance at 16 m/s:
ext{Reaction time} = rac{12 ext{ m}}{16 ext{ m/s}} = 0.75 ext{ s}Thus, the reaction time of the person driving the car is 0.75 seconds.
Step 3
Explain why the stopping distances are different for each speed in Fig. 20.1.
Answer
The stopping distances differ at varying speeds due to the combination of thinking distance and braking distance.
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Thinking Distance: This is the distance a car travels during the driver's reaction time. As the speed increases, the thinking distance increases linearly because the car covers more distance in the same amount of time.
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Braking Distance: This is influenced by the speed of the vehicle; it increases quadratically as speed increases. The kinetic energy of the car, which is proportional to the square of its speed, affects how far it needs to stop once the brakes are applied.
Therefore, at higher speeds, the total stopping distance (thinking distance + braking distance) increases significantly.