Aptitude - Problems on Trains - Discussion

Instead of 50/3 why we use 3/50?

It's (63-3) because they both are moving in the same direction. If they are opposite to each other at that time we add the relative speed.

Why we take (63-3) please explain anyone?

@Jeni.

The train and the man both were going in the same direction and that means by one hour when the train will have been going 63 km and the man 3km. So, the net distance will be 63-3 = 60km.

If they were approaching from the opposite direction, then we had to add up their speed.

Length of the train = 500m
Speed of the man = 3km/hr
Speed of the train = 63km/hr
Relative speed = 63-3 = 60km/hr = 60 * 5/18 = 50/3(m/s).
Let x be the sec,
500/x = 50/3,
X = 30sec.

It's 500 * 50\3.
= 500*3/50
= 10 * 3.
= 30sec.

I don't know how they calculate the speed of the train.

How come 5/18?

Tell me in details how it came?

Train Speed = 63 km/h = 17.5 m/s.
Man Speed = 3 km/h = 0.83 m/s.
Length of train = 590 m.

If the man and train and moving in the opposite direction then it will take less time to cross each other. If they are moving in the same direction then the train will take more time to cross the man and if the man is stationary then it takes time in between the cases discussed above.

Case 1: Let's suppose man is stationary i.e. Man speed = 0 m/s.
Time = Distance/Speed = 500/17.5 = 28.57 s.

Cast 2: If the man is moving with a speed of 0.83 m/s IN THE DIRECTION OF MOVING TRAIN
Relative speed = 17.5 + 0.833 = 18.33.
Time = Distance/Speed = 500/18.33 = 27.27 s.

Cast 3: If the man is moving with a speed of 0.83 m/s IN THE DIRECTION. " OPPOSITE" TO THE DIRECTION OF MOVING TRAIN.
Relative speed = 17.5 - 0.833 = 16.667.
Time = Distance/Speed = 500/16.667 = 30 s.

@Vicky.

In case 2.

We count the speed of man in the relative distance. Why don't we count the distance that the man travelled in finding the final time?

It should be 500+Dist Traveled by men.