Tuesday, October 4, 2016

Physics of NJ Train Crash



Recently a train crashed into a New Jersey terminal leaving 1 person dead and 114 others injured.  There have been a number of set backs in determining the cause of the accident, including a recovered event recorder that was not functioning.  One possible cause is user error meaning the train engineer did not slow the speed of the train to the 10 mph limit.  However, he claims that the train speedometer read 10 mph and that he was well rested with his phone off. 
            According to Wikipedia, when the emergency break is applied to a train the maximum deceleration is approximately 1.5 m/s2.  Assuming the well rested train engineer activated the emergency break and if the train had actually been going 10 mph, which is 4.47 m/s, then the distance required to bring the train to a complete stop can be calculated using Vf2 = Vo2 + 2a∆x.  Plugging in gives 0 = 4.472 + 2(-1.5)∆x and so ∆x = 6.7m. 

            Given the train went through barriers to collide with the wall, 6.7m seems unlikely to be the actual distance. As such the math indicates two possible scenarios, either the engineer did not apply the emergency break or the speed was not 10 mph.  If the other event recorder does provide usable data, it will be interesting to see what the cause of the crash actually was. 

http://www.amny.com/transit/hoboken-train-crash-engineer-claims-he-was-going-speed-limit-ntsb-says-1.12396539

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