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Difficulty: MediumStopping Distances

While driving on a well-maintained, dry road at a steady speed of 50 mph50\text{ mph} (80 km/h80\text{ km/h}), you suddenly need to bring your car to a complete stop in an emergency. According to The Official Highway Code, what is the standard braking distance under these conditions?

  1. A
    15 metres15\text{ metres} (50 feet50\text{ feet})
  2. B
    53 metres53\text{ metres} (175 feet175\text{ feet})
  3. 38 metres38\text{ metres} (125 feet125\text{ feet})Answer
  4. D
    76 metres76\text{ metres} (250 feet250\text{ feet})

Answer

38 metres38\text{ metres} (125 feet125\text{ feet})
According to The Official Highway Code, a car travelling at 50 mph50\text{ mph} (80 km/h80\text{ km/h}) has a total stopping distance of 53 metres53\text{ metres} (175 feet175\text{ feet}). This total consists of a thinking distance of 15 metres15\text{ metres} (50 feet50\text{ feet}) plus a braking distance of 38 metres38\text{ metres} (125 feet125\text{ feet}). Therefore, the braking distance alone is 38 metres38\text{ metres} (125 feet125\text{ feet}).

Step-by-Step Solution

1
Recall the components of total stopping distance at 50 mph50\text{ mph} (80 km/h80\text{ km/h}).
Total Stopping Distance = Thinking Distance + Braking Distance
Overall stopping distance is always divided into the driver's reaction phase and the vehicle's deceleration phase.
2
Identify the specific values specified by The Official Highway Code for 50 mph50\text{ mph} on dry asphalt.
Thinking distance is 15 metres15\text{ metres} (50 feet50\text{ feet}) and total stopping distance is 53 metres53\text{ metres} (175 feet175\text{ feet}).
Official standards establish fixed reference values under ideal dry conditions.
3
Calculate or isolate the braking distance component.
53 m−15 m=38 metres53\text{ m} - 15\text{ m} = 38\text{ metres} (125 feet125\text{ feet})
Subtracting thinking distance from overall stopping distance gives the exact distance required for the brakes to bring the vehicle to a halt.

Key Concept

Decomposition of stopping distance into thinking and braking components at 50 mph
Estimated Time:45s
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Topics

Stopping Distances

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