Aptitude - Problems on Trains - Discussion

Length of train(distance)=240m
Time=24sec
Formula: length(distance)=speed x time
240=speed x 24
speed=240/24
speed=10sec.

Now it has to pass platform of 650m
The total length of platform =650m
train length = 240m
The total distance the train pass the platform = 650+240=890m.
Because as the train entered the platform(650m) the train remaining part was outside the platform (240m).
So total distance the train cover is 890.

Here the aim of this problem is to be calculate the time taken of the train to cross 650 m long platform.

So from the given data (distance and time) , we have to calculate what is speed of the train.

(distance or length) / time = speed.

So we can calculate the value of speed.

You don't need to convert into hr. Because you are going to find out the time "in s" so you'll get the answer.

I hope anyone understand how do solve this kind of problems.

Well said Kumar.

Here 240m is the length of train, 650m is the length of Platform.

If we don't add 240m, we can only calculate the time taken by the part of engine to cross the bridge, not by the entire train.

That's why we are adding length of the train to platform length (distance = length of train + length of platform).

Reference: Important Formulas - Problems on Trains

Hi friends,

I tell you the exact reason for why we will and 240 with the plate from length.

Because after 65 seconds the head only reach the last point of the palate form but if the train crosses the plate form then the train will go 240 m ahead so the total meter will be 890. Or you want to calculate time.

So, the time will be 65 s to the platform and another 24 s to cross that platform.

So, it can also add as 65 s + 24 s = 89 s.

I think many people are confusing why we add train length here. The train crosses the bridge means that initially its engine was at starting of the bridge and when it has crossed the bridge, the last bogy of the train is on the other end of the bridge. And engine will be quite ahead by the length of train. So actually the train travels the distance 240+650 in this case when we consider only its engine for ease.

The answer has to be 89 seconds if it is given that this pole is a point of reference on the platform or bridge but is is not mentioned that pole is on the platform thus both the answers are correct it's a tricky question because of the language of the question (consider the question where we give conditions such as a man is standing on a platform that would help you to understand the concept better).

A train 240 m long passes a pole in 24 seconds. How long will it take to pass a platform 650 m long?

=====> for the tail of train to clear the platform it has to pass its own length + platform length.(240+650=890 m)

for 240 m. -- 24 sec.
for 890 m
by observation 890 is @ 4 times (some less) to 240
so time is also @ 4 times of 24 (some less) i,e. 96
from options 89 is @96 & somewhat less.

@Kartikey Patel & Devanshu
First Me too Think like this
if
train 240 m long passes a pole in 24 seconds.
i.e 240 m : 24 sec
then 650 m : ? sec
650*24/240=65

and the ans is 65sec
....
After Saiyam Explanation i got clearly...
bfe netu he expn.
"so we include train length utill its last coach passing the platform.
time considered up to its last coach left the platform."
Thanks...

The answer will be 65 only bcoz
train which is 240m long passes a pole in 24sec

so the speed of train is 240/24=10m/s

when speed of train is 10m/s then what time it will take to cross the platform which is 650m long i.e 650/10=65sec


two distance will be add when question will be like this

A train 240 m long passes a platform which is 650m long in 24 seconds the speed of train is?

Hi Saji,

You are wrong.

We have to add the length of the train to the length of the platform in order to find the time taken to 'cross the bridge'.


In case of crossing a man/post/pole:

Usually we will ignore the length of man/post/pole. If you want the result speed in 'milli meters/second' accuracy, you can add length of the man or pole to the length of the train.