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Difficulty: HardFactors Affecting Thinking Distance

A motorist travelling at 45 mph45\text{ mph} on a rain-soaked carriageway will experience a greater thinking distance than when travelling at 45 mph45\text{ mph} on a dry road, assuming their alertness and reaction time remain unchanged.

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Answer

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Thinking distance is the distance a vehicle travels during the driver's reaction time—the interval between identifying a hazard and physically applying the footbrake. It is calculated solely as the product of travelling speed and driver reaction time. Because the vehicle's speed (45 mph45\text{ mph}) and the driver's reaction time are identical on both roads, the thinking distance does not change. Rain and standing water reduce tyre-to-road friction, which doubles the braking distance, but have no mechanical impact on thinking distance.

Step-by-Step Solution

1
Recall the definition and formula for thinking distance in vehicle stopping dynamics.
Thinking distance is the distance travelled from the moment a hazard is perceived until the brakes are applied (dthinking=speed×reaction timed_{\text{thinking}} = \text{speed} \times \text{reaction time}).
Distinguishes the pre-braking human reaction phase from the post-braking mechanical deceleration phase.
2
Evaluate the variables given in the scenario.
The vehicle's speed (45 mph45\text{ mph}) and the driver's reaction time are identical in both wet and dry conditions.
Isolates whether any direct factor governing thinking distance has changed.
3
Determine the physical effect of the rain-soaked road surface.
Water on the road reduces tyre adhesion, which doubles braking distance, but has no physical effect on the distance covered before the driver presses the brake pedal.
Confirms that environmental surface conditions affect braking distance rather than thinking distance.

Key Concept

Thinking distance depends strictly on vehicle speed and driver reaction time; road surface conditions affect braking distance.
Estimated Time:1m 0s
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Factors Affecting Thinking Distance

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