Aptitude - Problems on Trains - Discussion

Let us suppose there is only a single train whose speed is (46-36)1OKM/H i.e 25/9 m/s ..

Now it takes 36 seconds to cover a certain distance.. so the distance would be {(25/9)*36} i.e 100 m.. therefore the distance covered by one train is 100m in 36 sec by the speed of 25/9m/s .


Now consider the question, there are two trains and their length is same..

So Train T1(46 KM/H) whose speed is higher than Train T2(36 KM/H) will cover 100m(Length of T1 and T2) that is 2L..(Suppose length of both trains is L)
therefore 2L=100
and L=50m

got my point?

We use this formula in that question

If two trains of length a metres and b metres are moving in the same direction at u m/s and v m/s, then:

The time taken by the faster train to cross the slower train = (_a+b)_____ sec.
(u - v)

but there is some changes in this formula when distance is same we use 2x where we use a+b as the distance of a+b two different distance

Why we need to subtract 46-36 and what is relative speed?

This is the simplest example of relative speed.

Hai how this 36 came? I didn't get it can you please explain clearly? why 2x? why 36 not 46?

I think answer is 100 because if we calculate x as 100m then the.

Another train length will be same because both are equal.

In the above problem it is given that the lengths of two trains are equal.

according to theory if both trains are moving in same directions then the lenghts will be subtracted but this is the case that both lenghts are different but in the above problem the lenghts are equal in this case we have to add lengths without regarding their directions so lenght is 2x

but as the trains are moving in same directions their relative speeds must be subtracted

so (46-36)*5/18
2x/(50/18)=36
2x=36*(50/18)
x=50m

How can we conclude that distance covered is 2x because here both the trains are moving and hence along with covering the distance 2x, they will cover some more distance. Please make this thing clear.

I can't get,please tell me, Why did we get 46-36? why didn't we get (46+36)

and why did we get 2x/36?

Please explain me.

Since the Trains are moving in the same direction The diff between their speeds has to be calculated.
46 kmph - 36 kmph = 10 kmph

convert into meters per second 10 x 1000 meters / 3600 seconds
We get 25/9.

Now apply formula distance = speed x time = 25/9 x 36
Cancelling 36 with 9 we get 4 multiply with 25 we get 100 meters, which is the length of two trains.
As per the question the two trains length is the same there fore each train length is 50 meters.