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

Question

I was driving along at 20m/s , trying to change a CD and not watching where I was going. When I looked up, I found myself 44m from a railroad crossing. And wouldn't you know it, a train moving at 29m/s was only 56m 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 0.43s , what minimum acceleration did my car need for me to be here today writing these words?

Explanation / Answer

time taken by the car to reach the crossing t1= 44 / 20 = 2.2s

time taken by the train to reach the crossing t2 = 56/29 = 1.93s

the time interval t = 2.2 - 1.93 = 0.27s

so the train and the car wil meet the crossing at this time. thus the car must accelerate much earlier than the reaction time. so the time difference must be 0.43 - 0.27 = 0.16s

thus the acceleration of the car = velocity of the car / 0.16 = 20 / 0,16 =125m/s2

Related Questions

Navigate

• Browse (All)
• Browse I
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.