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Stopping Distance + Reaction Time Problem -> Physics beginner

by MyFinalRegret
Tags: beginner, distance, physics, reaction, stopping, time
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MyFinalRegret
#1
Aug5-09, 04:30 AM
P: 2
1. The problem statement, all variables and given/known data
A car is traveling at 80km/h, and brakes with a reaction time of .5 seconds. The car decelerates at 8m/s/s, determine the stopping distance of the car.


2. Relevant equations

- V1 = V0 + at
- D = V0t + 1/2at2

Where:
V1 = Final Speed
V0 = Initial Speed
A = Acceleration
T = Time
D = Distance

3. The attempt at a solution

Distance Traveled before Braking:
80km/h = 22.22m/s

0.5 * 22.22m/s = 11.11 m

Distance After Reaction:
V1 = V0 + at
0 = 22.22 - 8t
t = 2.7775 seconds

D = V0t + 1/2at2
D = 22.22 * 2.7775 - [(8 * 2.77752)/2]
D = 30.86m

Total Stopping Distance = 11.11m + 30.86m
= 41.97 m

Notes
I am only beginning to learn some basic concepts of physics in class, so I'm not entirely sure about the equations.

My teacher has provided no answer sheet to the question, and I am finding it hard to grasp the method of solving the question without a step by step example from a similar question.

I'd greatly appreciate it if anyone could let me know if I am right, or how to do it if I am wrong.

Thanks :D
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Doc Al
#2
Aug5-09, 05:11 AM
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P: 41,459
Looks good to me--everything's correct.

FYI, there's another kinematic equation that relates velocity and distance directly for accelerated motion. That would enable you to combine a few steps. See: Basic Equations of 1-D Kinematics
MyFinalRegret
#3
Aug5-09, 06:57 AM
P: 2
Thank you for the help and additional formulas !
Now I'll be able to do my other sums :D


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