Aptitude - Problems on Trains - Discussion

The only thing to remember is that when objects are moving in the same direction,then relative speed is equal to subtraction of their respective speeds and when the objects are moving in opposite direction,then relative speed is equal to addition of their respective speeds.

Therefore, here v1 = 5 km/h, v2=?, t=10sec => 10/3600 hr.,
Distance = 125 mt => 125/1000 kms.

Now we know, Speed=distance/time.
or we can say, Relative speed = distance/time.

Since here relative speed= v2-v1 (objects moving in same direction).
Therefore, v2-5=125/1000 whole divided by 10/3600.

or, v2-5=125/1000 * 3600/10, on solving we get,
v2-5= 45 => v2 = 45+5 => V2=50 Km/hr.

Relative speed = x-5 (x is the speed of train).
(x-5)*5/18 = 125/10.
x-5 = 125*18/10*5.
x-5 = 125*9/25.
x-5 = 5*9.
x-5 = 45.
x = 50.

Hi @Swati look here let me explain:
L = Speed*time.

And,
Speed = length/time.
Length = 25/2.
Time = 5/18.

And,
25/2/5/18 = 25/2*18/5.
9*5 = 45km/hr.
x-5 = 45.

45+5 = x.
x = 50km/hr.

@Jothi,

x-5 = 45.
We add 5 to both sides so that we stay with x.

x-5+5 = 45+5.
Therefore,

So x = 50.

Why use 60*60/1000(18/5) I do not understand that?

I have a doubt on question. Whose speed is 5km/hr? either the man's or train's? please explain.

Why use 60*60/1000(18/5) I do not understand that?

Please explain.

125m/10s*18/5=45.

The man running in opposite direction at a speed of 5 km so 45+5=50.

How to be solve this 25/2*18/5 = 45?

It's simple way.

We know that the speed of train is 125m/10s.

Then 125/10 = 25/2.

This is the speed of train in 1 second.

Now speed in 1 hr = 25/2*3600 = 45.

And men is going in 5km/1hr so speed of train is 50km/hr.