Aptitude - Problems on Trains - Discussion

Solution:

Time = Distance/Speed.

Length of train=125m.

Speed of the person in the same direction is 5KM/hr i.e 25/18m/sec
the train takes 10 sec to cross i.e our time.

Let take x as the speed of the train.

So according to the above formula.
10 = 125/x-(25/18),
10 = 125 * 18/18x-25.
x = 13 * 18/5 m/sec.

To make it KM/hr we have to multiply it by the help of 18/5.
13*18/5 * 18/5 = 46km/hr.

So ans should be 46.

Why we should reciprocal 5/18 to 18/5? Please explain.

length = speed * time = 5 * 10 = 50.

The object Man is also moving in the same direction as that of the train so the total distance covered should not be 125 meters.

It should be the (125+X).

Where X is the distance covered by man in 10 seconds.

Good explanation, thanks.

I can't understand this sum please anyone explain me briefly.

What is the difference between the relative speed of train and the speed of the train? Anyone, please explain.

The train and the man are moving in the same direction we have to use subtraction.

Here, we have to find the value of X. So for that, we have to keep X separate either left side or right.

Shift 45 to left and x to right. Because we are shifting, the sign will be change (positive to negative & negative to positive).
x-5 = 45
-5 - 45 = -x
-50 = -x ....(- - = + , so - - canceled)
x = 50.

No, it's wrong!

At last, speed came 45km. Now since it's in the same direction hence we will subtract, right.

So S=S (train (since its bigger value) - the speed given (5) ) ==>45-5 = 40.


Speed cannot be negative hence we always subtract smaller speed value FROM bigger speed value in the case for the same direction!

First we write Data:

We Have D=125m t=10s,
S=D/t =125/10=25/2 m/s.

We want to convert from m/s to km/kr.
so we multiply 25/2 into 18/5,
@When we convert km/hr to m/s we multiply by 5/18,

@When we have to convert m/s to km/hr we multiply by 18/5,

Our answer are given in km/hr so we convert according_to by multiplying 18/5.

=25/2*18/5=45 Km/hr,

let we assume train speed be X.
And Man 5 km/hr.

If given in opposite direct then we add,

Here have in the same direction so we subtract,

x-5=45 So Answer is 50.