Wednesday, February 3, 2010

A motorist is traveling at 18 m/s when he sees a deer in the road 45 m ahead.?

A. If the maximum negative acceleration of


the vehicle is 鈭? m/s2, what is the maximum


reaction time t of the motorist that will


allow him to avoid hitting the deer?


B. If his reaction time is 1.40318 s, how fast will


he be traveling when he reaches the deer?A motorist is traveling at 18 m/s when he sees a deer in the road 45 m ahead.?
He'll hit the deer fast enough to squash it...





Pity, he could have had both lifes saved if he only have better reaction time...:-)A motorist is traveling at 18 m/s when he sees a deer in the road 45 m ahead.?
Since every second, the velocity decreases by 7m/s, you can say that 18 minus 7*(time it takes to stop)=0.


18-7t=0


Its algebra :)


t=2.57s





Assuming constant deceleration, his average velocity will be one-half his initial, hence avg v=9m/s





d=vt=(9.0)(2.57)=23.13m





He needs 23.13m to stop.





45-23.13=21.87m to apply brakes...


t=d/v=21.87/18=1.215s MAXIMUM RXN TIME





And if its 1.40318s,


he will have traveled 25.26m before applying the brakes.


(Below, v=final velocity ; (vo)=initial velocity ; x=distance ; (xo)=initial distance)





v^2=(vo)^2+2a(x-(xo))


v^2=18^2+2(-7)(0-25.26m)


v=5.44m/s





when he hits the deer

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