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Zorluk: OrtaStopping Distance Components

A combination vehicle equipped with an air brake system travels along an expressway at a constant speed of 45 mph45\text{ mph} (66 ft/s66\text{ ft/s}). The driver requires 1.75 seconds1.75\text{ seconds} for hazard perception, 0.75 seconds0.75\text{ seconds} for driver reaction, and 0.5 seconds0.5\text{ seconds} for air brake lag before the brake linings contact the drums and begin slowing the vehicle. What is the total distance, in feet, traveled by the vehicle from the moment the hazard appears until the mechanical brakes actively engage?

Cevap: 198 ft

Cevap

198 feet
Total stopping distance in an air-brake-equipped commercial vehicle comprises perception distance, reaction distance, brake lag distance, and effective braking distance. Prior to actual vehicle deceleration, the vehicle travels during perception (1.75 s×66 ft/s=115.5 ft1.75\text{ s} \times 66\text{ ft/s} = 115.5\text{ ft}), reaction (0.75 s×66 ft/s=49.5 ft0.75\text{ s} \times 66\text{ ft/s} = 49.5\text{ ft}), and air brake lag (0.5 s×66 ft/s=33 ft0.5\text{ s} \times 66\text{ ft/s} = 33\text{ ft}). Summing these three pre-braking components yields a total distance of 198 feet198\text{ feet}.

Adım Adım Çözüm

1
Determine the total pre-braking time by adding perception, reaction, and air brake lag durations.
1.75 s+0.75 s+0.50 s=3.00 seconds1.75\text{ s} + 0.75\text{ s} + 0.50\text{ s} = 3.00\text{ seconds}
Before the vehicle begins mechanical deceleration, distance is accumulated across three distinct pre-braking phases.
2
Calculate the individual component distances traveled at 66 ft/s66\text{ ft/s}.
Perception distance = 1.75 s×66 ft/s=115.5 ft1.75\text{ s} \times 66\text{ ft/s} = 115.5\text{ ft}; Reaction distance = 0.75 s×66 ft/s=49.5 ft0.75\text{ s} \times 66\text{ ft/s} = 49.5\text{ ft}; Brake lag distance = 0.50 s×66 ft/s=33.0 ft0.50\text{ s} \times 66\text{ ft/s} = 33.0\text{ ft}
Distance is the product of velocity and elapsed time for each phase.
3
Sum the component distances to find the total distance traveled before braking starts.
115.5 ft+49.5 ft+33.0 ft=198 feet115.5\text{ ft} + 49.5\text{ ft} + 33.0\text{ ft} = 198\text{ feet}
The total distance before active deceleration is the sum of perception distance, reaction distance, and brake lag distance.

Anahtar Kavram

Pre-braking stopping distance components for air brake vehicles include perception distance, reaction distance, and pneumatic brake lag distance.
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Stopping Distance Components

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