Aptitude - Problems on Trains - Discussion

x-5 is nothing but here x refers to the speed of train and as both train and boy are moving in the same direction relative velocity comes into picture and here relative velocity is the difference of two velocities.

To convert km/h into m/s we multiply that value with 5/18.why is this because
1km=1000m
1h=60min*60sec=3600sec
now
1km/h=1000/3600=5/18
if we want to convert m/s into km/h we have to multiply with 18/5.
hope you can understand.

Abisheks answer is realy nice. Thank you abi.

Just try this 1 sec 5 km/hr means 10 sec is 50 km/hr thats it..
becoz the man running at same time train is moving ..

125/10 = 25/2

25/2*18/5 = 450/10
45

friends,
i don't know how to solve this problems after this
so plz anyone help me out

It is brain storming and conceptual question .Thank you for giving more explanation on this question.Thank you very much....!

How/ why Let the speed of the train be x km/hr. Then, relative speed = (x - 5) km/hr.

Please any one explain me why let speed =(x-5)km hr.

Your running at a speed of 5km/hr
(1km=1000 meter and 1hr=3600seconds,which will be 1000/3600=10/36=5/18)
Note :for 1 km/hr
Therefore 5(given km)*5/18=1.39
-------------------------------
Meanwhile 125m long train crosses you in 10 seconds along with you in same diretion.
Then!!
125/10 i.e its in the form of (125)m/(10)s.
-------------------------------
So add those two values in the form of m/s,which is 13.89=a
-------------------------------
Now question to find speed of the train,since we found in the form of m/s,but the options provided are in the form of KM/HR
-------------------------------
So to convert M/S to KM/HR :
(a*18/5)=(13.89*3.6)
Gives answer as 50 km/hr

This is simple. Length of the train is given and the seconds is given.

So we have m/sec there. To convert it to km/hr,

1km= 1000 m and 1 hr = 3600 sec.

So km/hr= 1000/3600. So we have 18/5. Now we got our km/hr.

Well that guy is running at 5 km speed. So we take the train speed as x and subtracting the 5 km speed from that. We have x-5 as the train speed. Now x-5= 45. So x= 45+5=50. :-).

A Train 125m long passes a man,running at 5km/hr.

It means that train speed =5000m/3600sec.------(1hr=60*60=3600sec & 1km=1000meters).

& Second Train running on same Direction & Passed in 10sec's.

It means Second train cross distance within 10sec's.

Speed of Train for meters/10sec = 5000m/3600sec*10sec=1.388888888889m
So,that train speed for km/hr=speed of train for 10 sec * remaining 3590 Seconds(3600-10).
=1.3888888889*3590=49.8611111111111111=50km/hr.

Therefore, A speed of that train=50km/hr.