Aptitude - Problems on Trains - Discussion

The jogger is running at 9kmph.

240m ahead from 120m long train.

When the train covers 240m at speed of 45kmph in t = 96/5 sec in the same time the jogger covers 48m.

Since he is jogging at a particular speed so the total distance covered by the train to pass the jogger would be 120+240+48.

Then, how it could be 240 +120?

The jogger is running at 9kmph.

240m ahead from 120m long train.

When the train covers 240m at speed of 45kmph in t = 96/5 sec in the same time the jogger covers 48m.

Since he is jogging at a particular speed so the total distance covered by the train to pass the jogger would be 120+240+48.

Then, how it could be 240 +120?

The distance to be covered is the length from the train to the jogger (240) And we are adding 120 because we need to know the time when the whole train passes the jogger.

Why we have taken the distance covered by train as (120m +240m)? why to add the length of the track? Please explain.

When the train is moving towards the jogger the jogger is still running at 9Kmph or 2.5 m/sec so by the time the engine reaches 240mtrs the jogger would've moved forward.

Time taken for front of train to cover 240 mtrs = 24 secs (time = distance / speed{relative = 10 m/s})

Also the distance travelled by jogger in this 24 secs is = 2.5 mtr/sec * 24 sec = 60 mtrs
so in order for the train to completely pass the jogger, it has to travel 60 mtrs more.

Total distance = 60 + 120 = 180 m.
Speed = 10 m/s.
Time = 18 sec.

Total time = 18 + 24 = 42 sec.

Is this method is correct?

Speed of jogger=9km/h=9*(5/18)=2.5m/s.
Length=240.

Length of train = 120m.
Speed of train = 45km/h=45(5/18)=12.15m/s.

Relative Length=240+120=360m.
Relative speed=12.15-2.5=9.65m/s.

Speed = Distance/Time.
9.65 = 360/Time.
Time = 360/9.65.
= 36.

The jogger is ahead of the train by 240m and the question asks us to find the time train takes to pass the jogger, should we consider the time taken to cover distance of 240m and then add time take to cross the jogger.

How come 5/8? Please explain.

@All.

Please let me know why we have considered the complete length of the track, may be jogger is in half of the way or but the question here is train is crossing jogger, they are running in the same direction hence we have considered relative velocity but when the train is passing a jogger, jogger don't have any length. Please elaborate.

Why is the total distance taken as 240+120?