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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 can use the equation for acceleration:
We know:
- Initial speed () = 18 m/s
- Final speed () = 0 m/s (since the van comes to a stop)
- Deceleration () = -1.5 m/s² (deceleration is negative acceleration)
The change in velocity is:
Substituting into the acceleration equation gives us:
Rearranging to find time () gives:
Therefore, the time taken for the van to stop is 12 seconds.
Step 2
Explain how the stopping distance changes.
Answer
When a van travels on an icy road, the stopping distance is affected significantly due to reduced friction. The stopping distance is the total distance required to bring a vehicle to a stop after the brakes are applied.
- Reduced Friction: On icy roads, the grip between the tires and the road surface decreases. This means that the braking force is lower, leading to a longer stopping distance. The force can be calculated using:
Where 'm' is the mass of the van and 'a' is the deceleration. With less friction, the deceleration is smaller, leading to more time needed to stop.
- Thinking Distance: The reaction time of the driver also plays a role. On icy conditions, the driver may hesitate longer to respond due to fear of slipping, increasing the overall stopping distance. The stopping distance can be expressed as:
- Braking Distance: As less grip is available, even if the driver applies the brakes, the brakes may not be as effective, which contributes to increased braking distance on icy surfaces.
In summary, due to lower friction, longer reaction times, and reduced braking forces, the total stopping distance increases significantly on icy roads.
Step 3
Explain why this is dangerous for the people in the van.
Answer
If the van crashes after a short stopping time, the danger to the occupants is heightened because they may not have enough time to brace for impact. Several factors contribute to the danger:
- Increased Impact Force: A shorter stopping distance means that the van comes to a sudden halt, leading to a higher impact force experienced by passengers. The relationship can be understood from Newton's second law, where:
A rapid deceleration results in a greater force acting on the body.
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Inertia Effect: Inside the van, passengers continue to move forward due to inertia. If the van stops suddenly, they may be thrown forward, potentially causing injury against seatbelts or dashboards, even if belted.
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Lack of Time to Prepare: In a slow descent to a stop, people have time to brace themselves for the impact. However, a sudden stop can prevent this preparation, increasing risks of injuries.
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Shock and Panic: In emergencies, a sudden stop can cause shock and panic among passengers, impairing their ability to respond effectively to the situation.
In conclusion, a shorter stopping distance in a crash is dangerous because it increases the risk of severe injuries or fatalities to the passengers due to higher forces experienced during impact and inertia.