Aptitude - Problems on Trains - Discussion

"A jogger running at 9 kmph alongside a railway track in 240 metres ahead of the engine" - This means The engine is 240 metres behind of that person. So the train has to cover that distance (120+240) metres by it's own speed (without considering relative speed as it has not reached that jogger yet) and after that train has to cover that jogger (considering relative speed).

When the train is covering (120+240) metres the jogger has moved some extra distance in forward direction by that time. So thinking in that way is going to be more complex.

Here we have to think of two moving objects - one is the train which is of length 120 metres and of speed 45Kmph. Another is of length 240 metres and of speed 9Kmph in Same Direction. (Like two trains moving in same direction with different speed).

So, total length = 240+120 = 360 metres.

Relative speed = (45-9) Kmph = 36*(5/18) m/s = 10m/s.

Hence time = 360/10 = 36 seconds.

For same direction,

t=l1+l2/s1-s2.

How come 5/8? Please explain.

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?

Because if two trains run in the same direction the Speed of train will decrease to pass another train.

Y DID U substract 45-9? i didn't understand

If in both the objects move in the same direction, the relative speed would be the sum of both the speeds. How is calculation is done. Even if tried with the mentioned procedure, the options don't have the derived answer

Jogger is not idle. He also running. So we done this step 45-9km/hr.

9km/hr is jogger speed.

Relative speed= hidh speed + low speed when the objects are moving in the oppsite direction
Relative speed= hidh speed - low speed when the objects are moving in the same direction

Yes, karthik is right.