How Does Human Reaction Time Affect Car Stopping Distances?

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SUMMARY

The discussion focuses on calculating stopping distances for a car traveling at an initial speed of 85 km/h (23.61 m/s) with a human reaction time of 1.0 second under two different deceleration rates: -4.0 m/s² and -8.0 m/s². The user correctly identifies the need to convert speed and applies the formula for distance, d = (v1 + v2)/2 * t, but encounters issues with time calculations. The stopping distances calculated were 82 meters for -4.0 m/s² and 47 meters for -8.0 m/s², indicating a misunderstanding of how to incorporate reaction time into the total stopping distance.

PREREQUISITES
  • Understanding of basic kinematics, specifically the equations of motion.
  • Familiarity with unit conversions, particularly between kilometers per hour and meters per second.
  • Knowledge of how to calculate average speed and time.
  • Ability to apply the concept of reaction time in physics problems.
NEXT STEPS
  • Review the kinematic equations, particularly d = (v1 + v2)/2 * t.
  • Learn about the impact of human reaction time on stopping distances in driving scenarios.
  • Explore advanced topics in physics related to deceleration and stopping distances.
  • Practice problems involving different speeds and deceleration rates to solidify understanding.
USEFUL FOR

Students studying physics, particularly those focusing on kinematics and real-world applications of motion, as well as educators looking for practical examples of how human factors affect vehicle dynamics.

JDR 007
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Homework Statement



Determine the stopping distances for a car with an initial speed of 85 km/h and human reaction time of 1.0 s for the following accelerations.
(a) a = -4.0 m/s2
m
(b) a = -8.0 m/s2
m

Homework Equations


d=v1+v2/2 *t
a=change in velocity/time

The Attempt at a Solution


I converted 85kh/h into 23.61m/s
I found how many seconds in each instance
(a) 5.9s...I did -4=(0-23.61)/t solved for t
(b)2.95s...same as a
using these times I used (23.61+0)/2 *Time then added 1 for the reaction delay

I got (a)=82 and (b)=47

What am I doing wrong?
 
Last edited:
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Subtract time.
 

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