Aptitude - Problems on Trains - Discussion

How he equated 45 to x-5?

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

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.

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

So numerator and denominator will be interchange.

Why we relate the speed of man and train length?

Why relative speed? They asked only speed?

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

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.

@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.

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

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