Aptitude - Problems on Trains - Discussion

The train and the man are moving in the same direction and hence for the train to catch up and pass. The man it should first overcome the speed of the man that is 3km/hr and hence that's why we subtract 3 from 63kms/hr which is the speed of the train.

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.

@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.

Instead of subtracting 63-3, I first converted 63kmph and 3kmph to its equivalent m/s and then I subtracted. The answer I got was not equal to 60*(5/18). Why? Can someone explain?

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.

@Smith.

In this type of problems, you can consider one object (train or man) is steady and give the velocity of that steady object give to another object.

If they are in the same direction than minus and if the direction is opposite than add the velocities.

After converting 60km/h to m/s.
We want to find the time t = l/s.
T=500/50/3.

3 is in the denominator.

Denominator of the denominator goes to the numerator then we get 500*3/50=30.

Why 50/3 is taken as 3/50?

@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.

Same direction man&train moving = a+b/u-v.

500/63-3*5/18 m/sec.

=> 30 sec.