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A van travels along a road at a constant speed - OCR Gateway - GCSE Physics - Question 22 - 2021 - Paper 1
Question 22
A van travels along a road at a constant speed. (a) The van brakes and decelerates at a constant rate: - The initial speed of the van is 18 m/s. - The deceleration... show full transcript
Worked Solution & Example Answer:A van travels along a road at a constant speed - OCR Gateway - GCSE Physics - Question 22 - 2021 - Paper 1
Step 1
Calculate the time taken for the van to stop.
Answer
To find the time taken for the van to stop, we need to use the equation:
a = \frac{\Delta v}{t}$$ Where: - $a$ is the acceleration (deceleration in this case, which will be negative), - $\Delta v$ is the change in velocity, - $t$ is the time taken. Given: - Initial speed ($u$) = 18 m/s, - Final speed ($v$) = 0 m/s, - Deceleration ($a$) = -1.5 m/s². The change in velocity is:\Delta v = v - u = 0 - 18 = -18 , \text{m/s}.
t = \frac{\Delta v}{a} = \frac{-18}{-1.5} = 12 , \text{s}.
Step 2
Explain how the stopping distance changes.
Answer
The stopping distance can be influenced by various factors, especially when the van is on an icy road. On ice, the friction between the tires and the road surface is significantly reduced, which increases the stopping distance compared to a dry road. The factors include:
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Reduced Traction: On icy roads, the tires have less grip, making it harder for the vehicle to slow down effectively. This can lead to longer stopping distances.
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Braking Distance: The distance required for the vehicle to come to a complete stop increases significantly. For example, while the stopping distance on a dry surface may be shorter, it may almost double on ice, depending on how slippery the surface is.
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Driver Reaction Time: The time it takes for a driver to react to a hazard may also change. On an icy road, the fear of losing control may alter the driver's reaction, potentially causing them to brake harder or later than they would on a dry surface.
In conclusion, the combined effects of reduced traction, longer braking distances, and variable driver reactions contribute to increased stopping distances on icy roads.
Step 3
Explain why this is dangerous for the people in the van.
Answer
When the van crashes, the time taken to stop is much smaller, which is inherently dangerous for several reasons:
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Impact Force: A sudden stop means a higher impact force on the occupants of the van. If the van hits an object or another vehicle, the violent deceleration can cause serious injuries or fatalities due to the rapid change in momentum.
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Lack of Preparedness: If passengers are not braced for a quick stop or crash, they may be thrown forward, increasing the risk of injury. This unpredictability adds to the danger as the passengers might not have time to react.
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Shorter Reaction Time: In emergency situations, a shorter stopping distance may not give enough time for drivers to react adequately to an impending collision, increasing the risk of accidents.
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Use of Safety Features: Modern vehicles are equipped with safety features like seatbelts and airbags intended to protect passengers during a crash. However, in instances where the stopping distance is exceedingly short, these safety measures may not be effective enough to prevent injury or death.
Overall, the combination of high inertia, sudden stops, and lack of adequate time to react makes crashes particularly dangerous, significantly increasing the risk of serious harm to those inside the van.