Aptitude - Problems on Trains - Discussion

In this problem the question is how much time it take to cross the jogger why are you considering the plat form length?

In any problem we will need to keep all the values in an uniform form, i.e. either all must be in m/sec or KM\hr.

In this problem they have converted from Km\Hr to m/sec. Therefore we multiply it my 1000/3600 (1 km = 1000 meters and 1 hour = 3600 seconds). When we cancel numerator and denominator we get, 5/18. This is how we get 5/18. Hope it helps.

How 5/18 will came? Please clarify.

Suppose jogger is running at 18 kmph and rest things are same so according to the calculation as done in explanation time should be 360/(15/2) = 48 sec but in that time jogger have also run 48*5 = 240 m so yet 120 m ahead of train.

The jogger is not idle eight, I think it is wrong because the jogger will run at a speed of 9 kmph during the time the train passes him so this distance should also be covered I solution but it is not the answer would be 48 sec.

In how much time train crosses the jogger?

Then why they are adding the 240 m railway track length?

Jogger speed, train speed, train length enough. Please any one solve my doubt.

t = a+b/u-v.

The jogger is also running. So, we also need to factor in the additional distance he covers.

If the time taken by train to cross the jogger is x.

(360+(9*5/18)*x)/10 = x.

x = 48 sec.

For the 1st 240m. Why are calculating the relative speed?

The jogger comes alongside the train after 240m. So, after that the relative speed should be considered. Please explain.

"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.