Aptitude - Problems on Trains - Discussion

Use formula
L=length S=Speed
(L1+L2)/(S1-S2)=Time taken by fast train to cross slow train

Let length of train be x
Relative speed = (46-36) * 5/18 m/s =50/18
(x+x)/(50/18) = 36
2x/50=2
2x=100
x=50.

In the question it's clearly mentioned two trains are of same length.

So we can use formula , two trains or two objects bodies are moving in the same direction at u m/s and v m/s, where u > v, then their relative speed is = (u - v) m/s.

* So 46-36=10km/hr.
* 10 *5/18 : 25/9
* 25/9*36 :.100 ( both train )
* 100/2=50 each train.

Thanks.

What is relative speed?

Should be mentioned that the faster train started behind the slower train.

It should be mentioned that the faster train started behind the slower train.

If both trains are started at same place then we do not get 2x, because faster train only cover x area which is his own length.

If a train has the length x and the other train of same length cross the train of length than distance travel by it must be x so my query is why we are taking length 2x instead of x. Please tell.

Length of the trains be x & 2x because after 36 second the faster train is going to pass the slower train. At that time faster train covers 460m and slower train covers 360m. The difference is 100m. This difference is between faster train's front edge and slower train's back edge.

Then it involves the distance of both the trains, hence we need to divide 100m by 2 (because in the question they've given as both the trains of equal length) to get the length of the train.

I didn't understand that why we are considering speed of slower train even its mention that faster crosses the slower one.

Why did you take 36 again two times please explain?

I think we can do it in a different way.

Distance = Speed*Time.

= (46-36) *5/18*36.

= 100.

This is the length of two trains.

And it is given that length of both the trains are equal.

Therefore length of one train is equal to 50.

Please some one suggest that it is correct or not.