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## Homework Statement

Tests reveal that a normal driver takes about 0.75 s before he or she can react to a situation to avoid a collision. It takes about 3 s for a driver having 0.1% alcohol in his system to do the same. If such drivers are traveling on a straight road at 30 mph (44 ft/s) and their cars can decelerate at 2 ft/s2, determine the shortest stopping distance d for each from the moment they see the pedestrians. Moral: If you must drink, please don’t drive!

## Homework Equations

s=vt

y

^{2}= y

^{2 }+ 2ac (s - s0)

## The Attempt at a Solution

I already know how the book solves it, the problem is that I'm not sure if the book is correct. Here's the solution from the book (12-15):

http://image.slidesharecdn.com/solutionmanualhibbelerengineeringmechanics12thedition-130719121523-phpapp02-131228081729-phpapp02/95/solutionmanualhibbelerengineeringmechanics12thedition-10-638.jpg?cb=1388219005 [Broken]

But the problem is that I think they gave the distance d relative to some coordinate where s=0 at t=0 and not the d that is illustrated. I think that the proper solution for this is something like this:

let the distance they got at time t=0.75s be d1=33ft and the solution they obtain is d2=517ft. Now this are relative to the origin s=0, t=0. So the distance that we want to find "d" is d=d2-d1=484ft. Same procedure for the 2nd case. Am I right?...I think the illustration is for the breaking distance, isn't it?

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