Crash Course
I guess it's high time for another blog contest. Getting no response to my last one was a bit rough, but I think I've gotten over it! This one comes straight out of the news. If it was in the Tribune, you know its true!
An Amtrak train recently crashed into a freight train, injuring 60 people. This report says that the train was speeding by a substantial amount. Given the data from the report, describe what would likely have happened had the train been going at the speed limit (15 mph) rather than its actual speed (40 mph) at the time that the freight train was sighted. (Be sure to state any assumptions that you make why you think they are valid). Would there still have been a crash? How fast?
Best answer before the Christmas party (Dec 20, 11:30 am) wins Whitey's!
3 comments:
OK, so this is pretty funny actually. When this story broke--so the day the day the two trains hit--I was ON AN AMTRAK TRAIN coming back from Washington State. (you have not experienced amtrak until you have had the joy of riding one for 40 hours across most of the continental united states). Anyways, due to my obvious expertise in the matter, of 80+ hours on an Amtrak train, I have come to realize that one, as a passenger you want the train to be going as fast as possible, and two, the Amtrak yields to the freight train. EVERY single time we saw a freight train we would stop so it could go wooshing on by. That being said, it is possible that if the Amtrak was going 15mph like it was supposed to that it would have been able to stop sooner because of its decreased velocity and then no crash would have occured. But what I want to know is how do you not see the other train? The front of an Amtrak train is all glass and flat so its not like they could argue low visability. Maybe the tracks were to wet because there was an ice storm the day of.. or MAYBE the tracks were actually icey themselves, Because as physics geniuses we all realize that if the coefficient of friction on the tracks is changed due to a friction "reducer" like ice, then the train would not be able to stop and then CRASH! into the other one.
So yeah... thats why the trains crashed... because the drivers are stupid.
Kristen:
Hope you had a DS or a good book or something to pass the time!
John took the Amtrak home for Christmas. Last year, the brakes iced over, and the train had to wait on the tracks in the middle of nowhere while they thawed them with a blowtorch. Ah, the fun of transportation.
Yay! Kristen wins Whitey's!
Yes, indeed, if the train had been going at the speed limit, they would likely have been able to stop in time.
I assumed that the train would be able to slow down with the same acceleration, whether it was going fast or slow. As Kristen said, that depends on the frictional force, which depends on the conditions of the track, not the speed.
With that assumption, we have the equations
v^2 - vo^2 = 2ad
and
v'^2 - vo'^2 = 2ad'
where the prime refers to the hypothetical train going at the speed limtit.
These equations can be written as
d'/d = (v'^2 - vo'^2)/(v^2 - vo^2)
Can the train stop before hitting the other train? If it stops v'=0.
Plugging in that, and vo=40mph, v=35 mph, vo'=15 mph, we find
d'/d = 3/5
That means, if the train were traveling at the speed limit when it began to brake, it would have stopped only 3/5 of the way to the other train.
No train wreck, yay!
Post a Comment