Aptitude - Problems on Trains - Discussion

How the will be 50?
Speed = 25/2(m/s).

Converting(m/s)to(km/hr).
25/2*18/5 = 45.

@Hemavathy. Since man is moving in same direction with train the relative speed is s-5 so,

s-5 = 45.
s = 50 km/hr.


Suppose if man move in opposite direction of train then,

s+5 = 45.
s = 40 km/hr.

Length of the train = 125 m.
Speed of the man = 5 km/hr.
Speed of the man in meters = (5*1000)/(60*60)=(50/36)=(25/18).
=1.388 m/sec.

Since train has covered the distance in 10 secs.
Let us calculate the distance covered by the man in 10 secs.
distance covered by the man in 10 secs = 13.88 m.

Therefore the displacement(d) = 125 m+13.88 m = 138.88 m.

Speed of the train = (138.88/10) = 13.88 m/s.

Therefore The Speed of the train in Hours = 13.88 * 60 * 60 = 50000 m/sec = 50 Km/hr.

Train is same dxn and man is also some dxn it means it means speed is minus x-5 = 125/10*18/5 = 50.

Why we relate the speed of man and train length?

Why relative speed? They asked only speed?

1 km = 1000 m/1 hr = 3600 sec = 5/18 but we want to convert just opposite.

So numerator and denominator will be interchange.

We have added the 5 km/hr to the final answer because the speed that comes out is with respect to man and to calculate the actual speed of the train we have added 5 km/hr to the final answer.

X-5 = 45 is right because train and man same side. In same side it is correct.

How he equated 45 to x-5?