Aptitude - Problems on Trains - Discussion

Train Length 240m long.
Time to pass pole = 24 second.

Speed= 240/24=10 m/s.

For length 650 m = 240+650=890m.
Speed = 890/10=89.

We add both the length of the train and platform because the train has to cross also its tail from the platform. If, the only head of train (engine) crosses the platform its other parts remain on the platform.

I think answer is 65 sec. Because there is not mention total time.

Hey, Dude, I am here to clarify your Doubt.
Here Given data is :
Length of the Train = 240m.

Time is taken by the train to cross the pole = 24sec.
so speed of the train = distance/time.
=> 240/24 = 10m/s.

Therefore train speed = 10m/s.
And Length of the platform = 650m.

So we can add the length of train+length of the platform=240+650 = 890m.

bcoz train passes the platform that y we can add both the lengths here.
time is taken by train to cross the platform=total distance/speed.

So 890/10 = 89sec.

Length of the train is 240m.

Length of the platform is 650m.

How can you compare train length and platform length? Time taken can be calculated by adding length of the platform and the train.

Answer 65 is correct because the question asks only about platform.

Why do you add 240?

I think 65 is the correct answer.

And why we add 240 +650?

240 mtrs -- 24 sec.
890 mtrs-- x sec.

ie..890 * 24/240 = 89 sec.

240÷10 = 24.
650÷10 = 65.
65 + 24 = 89.

We need to find the time that will take to pass a platform of 650 m.

Therefore, Time = Distance/Speed.
Speed is not given so need to find speed with given values.
Speed = Distance / Time.
= 240 m/24 sec.
= 10 m/sec.

Now we have Distance and Speed to calculate Time that will take to pass 650 m platform.
Time = (650 + 240)m/10 m/sec.
= 890/10 sec.
= 89 sec.

Note : If a train passes a tunnel, bridge, platform then distance covered by train is Length of the train + Length of tunnel (or) bridge (or) platform.

That's why we are adding Length of train + Length of the platform in Distance while calculating Time.

Should not consider the only Length of the platform(650 m).