Fig. 20.1 shows thinking, braking and stopping distances for the same car travelling at different speeds. Speed (m/s) Thinking distance (m) Braking distance (m) Stopping distance (m) 8 6 12 18 16 12 24 36 32 24 96 120 Fig. 20.1 (a) Describe how the thinking distance changes when the speed doubles. Use data from the table in your answer. (b) Calculate the reaction time of the person driving the car. Answer = ........................... s (c)* Explain why the stopping distances are different for each speed in Fig. 20.1.

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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) Thinking distance (m) Braking distance (m) Sto... 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.

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Answer

The thinking distance is directly proportional to the speed of the car. Referring to the table, when the speed increases from 8 m/s to 16 m/s, the thinking distance changes from 6 m to 12 m, which is an increase of 6 m. Furthermore, when the speed increases from 16 m/s to 32 m/s, the thinking distance goes from 12 m to 24 m. This illustrates that as the speed doubles, the thinking distance also doubles.

Step 2

Calculate the reaction time of the person driving the car.

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Answer

To calculate the reaction time, we can use the formula:

$ext{Reaction time} = \frac{\text{Thinking distance}}{\text{Speed}}$

Using the data for a speed of 16 m/s and a thinking distance of 12 m:

$\text{Reaction time} = \frac{12 \text{ m}}{16 \text{ m/s}} = 0.75 ext{ s}$

Step 3

Explain why the stopping distances are different for each speed in Fig. 20.1.

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Answer

The stopping distance of a vehicle at any speed is the sum of the thinking distance and the braking distance. As speed increases, both the thinking and braking distances increase due to several factors.

Thinking Distance: This part of the stopping distance increases with speed, as a faster car covers more distance in the same time frame while the driver processes the need to stop.
Braking Distance: The braking distance depends on the speed of the vehicle and is influenced by the kinetic energy of the car. Kinetic energy increases with the square of the speed, expressed as:

$ext{Kinetic Energy} = \frac{1}{2}mv^2$

As the speed increases, more energy is required to bring the vehicle to a stop, resulting in longer braking distances.

Combining both factors, as speed increases, the total stopping distance is significantly larger because both components increase, leading to higher overall stopping distances at higher speeds.

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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

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

Describe how the thinking distance changes when the speed doubles.

Calculate the reaction time of the person driving the car.

Explain why the stopping distances are different for each speed in Fig. 20.1.

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