What is the spead of train?

[Guest]

In a Tunnel 1 KM long. Two friends are standing at 600m inside the Tunnel (i.e. 600m from 1 side and 400m from other).Suddenly they heard the whistle of a train.Both started to run on opposite direction at spead of 10 KM/Hr.Both of them just survived.

What is the spead of train?

[Guest]

Good point and not really nit-picking. The speed must be something less than 50kph.

Or does it? What if the first person exits the tunnel and the train arrived a split second later and then, traveling at 50 kph, the other kid would just get out of the way in time.

The only thing that matters here is the distance covered and the speed at which the train would need to go from the first kid's encounter to the second kid's encounter. And we know that one - it's one km and it has to go 50 kph because otherwise the second kid would not have a "near miss."

Edited August 7, 2008 by IdoJava

[Guest]

Slow.

[Guest]

when whistle blows:

[-----.-----.-----.-----.AB-----.-----.-----.-----.-----.-----]

400m 600m

when train reaches tunnel, both lads have run 400m

AT[-----.-----.-----.-----.-----.-----.-----.-----.B----.-----]

800m 200

When train reaches End of tunnel

AT[-----.-----.-----.-----.-----.-----.-----.-----.-----.-----]TB

So the train moves has to move 1000m in the time it takes the second

lad to move 200m. This is 5 times faster, or 50KM/h

[Guest]

they're both just both in another tunnel! they heard the whistle of train..but not on the tunnel they are in. lol.

that's why they were both survived.

[Guest]

Or does it? What if the first person exits the tunnel and the train arrived a split second later and then, traveling at 50 kph, the other kid would just get out of the way in time.

The only thing that matters here is the distance covered and the speed at which the train would need to go from the first kid's encounter to the second kid's encounter. And we know that one - it's one km and it has to go 50 kph because otherwise the second kid would not have a "near miss."

I was going to answer the same - "just less than" - until I heard this explaination...

GOOD RIDDLE!

[Guest]

QED (Quite Easily Done)

I'm not sure if you were kidding, but QED is "quod erat demonstrandum;" Latin for "that which was to be demonstrated."

[Guest]

Hows about they ran to the walls and missed the train? therefore the speed wouldnt matter

as in if the train is ^ the tunnelwalls are | | and the people are < and >

|< ^ >| and the train misses them. it fits all of the requirements, so would this work?

Unfortunately, there is never a guarantee that there will be more than a few inches clearance between the train and the tunnel wall. When you look at train tracks, they are 4ft 8.5in wide from the inside of the rails. This is simply where the wheels ride; you must take into account another 4ft on either side for the overhang of most rail cars. Tunnels are built just wide enough for the trains and are not designed with pedestrian traffic in mind. After all, it is trespassing to be walking along the train tracks and could very well get you killed. Trains are a lot quieter than you think, hence the whistles. Take my advise, stay off any rail tracks.

[Guest]

In a Tunnel 1 KM long. Two friends are standing at 600m inside the Tunnel (i.e. 600m from 1 side and 400m from other).Suddenly they heard the whistle of a train.Both started to run on opposite direction at spead of 10 KM/Hr.Both of them just survived.

What is the spead of train?

If the friend running towards the train survived then the train obviously had not entered the tunnel yet or was stopped inside the tunnel,,, if the train was moving toward the tunnel, how far away was it when the whistle was heard.... if not moving who cares. Most likely though, they were standing in line in the dinner car of the train...

[Guest]

The speed of the train doen't matter if it takes more than 3min and 10sec to reach any side of the tunnel. Thats the simplest answer. In this case, both friends had already reached the end of the tunnel, and the train could enter it from any side without problems.

[Guest]

No. I still feel the diretion of where the train should be made known.

Now you have the perception of the train coming in at 50kph against the 400m person. Now what if the train is coming in against the 600m person? true that with 50kph, both people will still survive but with 100kph or maybe even to 200kph, if the 600m men survived, the 400m have already pass the test.

So your answer of 50kph would be wrong in this sense.

therefore, i still feel that the direction should be announced together with the question. We cannot assume things and then another way it went utterly wrong.

[Guest]

Another way of looking at the puzzle:

what if the friends did not run along the length but the breadth of tunnel, towards the wall in opposite direction??

the speed of the train now can be anything???

[Guest]

Here's how I look at this:

The first traveled .4 km at 10km/hr. This means it took him .04 hrs to get to the end of the tunnel. this is 2.4 minutes.

The second guy traveled .6 km at 10km/r. This means it took him .06 hrs to get to the end of the tunnel. this is 3.6 minutes.

Assuming the train got to the entrance of the tunnel just as the first guy entered, the train must travel the full kilometer in 1.2 minutes to just miss the second guy. 1km/1.2min = 10km/12min = 50km/60min or.... 50km/hr.

The direction of the train is irrelevent. We are told that both survived. This means that the train MUST have been coming from the direction of the closer end of the tunnel. If it were going the other direction, one of the men would have died because they were running the same speed, or the second guy would have been easily out of the tunnel LONG before the train exited the tunnel. The problem clearly states that they both JUST survived indicating it was a close call for each of them.

Edited December 21, 2011 by revathiest