2 (a) Figure 3 is a speed limit sign from a European motorway. The speeds shown are in km/h (kilometres per hour). The sign tells drivers to drive at a slower speed in wet weather. Explain why it is safer for drivers to drive at a slower speed in wet weather. (ii) Show that a speed of 31 m/s is less than a speed of 130 km/h. (iii) The driver’s reaction time is the time between the driver seeing an emergency and starting to brake. A car is travelling at a speed of 31 m/s. The car travels 46m between the driver seeing an emergency and starting to brake. Calculate the driver’s reaction time. Give your answer to 2 significant figures.

GCSE Edexcel Physics Combined Science Density ρ: 2 (a) Figure 3 is a speed limit

2 (a) Figure 3 is a speed limit sign from a European motorway - Edexcel - GCSE Physics Combined Science - Question 2 - 2022 - Paper 1

Question 2

2 (a) Figure 3 is a speed limit sign from a European motorway. The speeds shown are in km/h (kilometres per hour). The sign tells drivers to drive at a slower speed... show full transcript

Worked Solution & Example Answer:2 (a) Figure 3 is a speed limit sign from a European motorway - Edexcel - GCSE Physics Combined Science - Question 2 - 2022 - Paper 1

Step 1

Explain why it is safer for drivers to drive at a slower speed in wet weather.

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Answer

Driving at a slower speed in wet weather is safer due to several factors. Wet road conditions can reduce tire grip, leading to a higher chance of skidding or losing control. Additionally, wet weather usually results in decreased visibility, making it harder for drivers to see hazards. A slower speed ensures longer braking distances, allowing drivers more time to react to unforeseen circumstances.

Step 2

Show that a speed of 31 m/s is less than a speed of 130 km/h.

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Answer

To show that 31 m/s is less than 130 km/h, we can convert 31 m/s to km/h:

$1 ext{ m} = \frac{1}{1000} \text{ km}$ $1 ext{ s} = \frac{1}{3600} \text{ h}$

Therefore, $31 ext{ m/s} = 31 \times 3600 \text{ h} = 111.6 \text{ km/h}$

Since 111.6 km/h < 130 km/h, 31 m/s is indeed less than 130 km/h.

Step 3

Calculate the driver's reaction time.

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Answer

To calculate the driver's reaction time, we use the formula:

$\text{Distance travelled} = \text{Average speed} \times \text{Time} \Rightarrow \text{Time} = \frac{\text{Distance travelled}}{\text{Average speed}}$

Substituting in the values:

$\text{Time} = \frac{46 \text{ m}}{31 \text{ m/s}}$

Calculating the result:

$\text{Time} \approx 1.48 \text{ s}$

Rounded to 2 significant figures, the reaction time is approximately 1.5 s.

2 (a) Figure 3 is a speed limit sign from a European motorway - Edexcel - GCSE Physics Combined Science - Question 2 - 2022 - Paper 1

Worked Solution & Example Answer:2 (a) Figure 3 is a speed limit sign from a European motorway - Edexcel - GCSE Physics Combined Science - Question 2 - 2022 - Paper 1

Explain why it is safer for drivers to drive at a slower speed in wet weather.

Show that a speed of 31 m/s is less than a speed of 130 km/h.

Calculate the driver's reaction time.

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