I was driving along at 20 m / s , trying to change a CD and not watching whttp:/

Question

I  was driving along at 20 m/s, trying to change a CD and not watching whttp://www.chegg.com/homework-help/askhere  I  was going. When  I  looked up,  I  found myself 43m  from a railroad crossing. And wouldn't you know it, a train moving at 30m/s  was only 60 m from the crossing. In a split second,  I  realized that the train was going to beat me to the crossing and that  I  didn't have enough distance to stop. My only hope was to accelerate enough to cross the tracks before the train arrived.

If my reaction time before starting to accelerate was 0.49s , what minimum acceleration did my car need for me to be here today writing these words?

Explanation / Answer

Train will take

t = 60 / 30

= 2 sec.

to reach the crossing.

I have to travel 43 m in 2 sec.

20 * 0.49 + 20*(2 - 0.49) + (1/2)a * (2 - 0.49)^2 = 43

40 + 1.14a = 43

a = 2.63 m/s^2

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