Aptitude - Problems on Trains - Discussion

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

This is the simplest example of relative speed.

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

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

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?

Here what is mentioning by 18/5 or 5/18... have some confusion

How the relative velocity is V2-V1? Since tthe trains are in same direction, velocity shall be V1+V2

"The faster train passes the slower train in 36 seconds" as mentioned in Question i.e First Train is behind the second Train and it crosses second train in 36 sec.

Therefore distance travelled in 36 sec is, length of second train and also length of first train. Hence the distance is 2x.

How can we take 2X there?

The 2x is bcoz

Let the length of the train a =x

Length of the train b =y since both the trains are equal in length uwe can take
Length of train b as also "x"
So, Distance=x+x=2x

simple :-)