Aptitude - Problems on Trains - Discussion

When the two trains start running with different speed, the speeder train will get ahead of the slower train at some time.

With both the train running, it is hard to find the distance after which the speeder train completely pass the slower train.

To make it easy, find the relative speed of the train. It is 4km/hr. It can be said that when the slower train speed is 0km/hr, the speeder train speed is 4 km/hr.

Assume the slower train stops or consider it as a platform, then the speeder train cross the slower train in 36 seconds @ 4km/hr. Here the total distance covered is length of speeder train and the platform (slower train)

Have a good day.

The distance covered is (X+X) = 2X.

Let, the speed of 1st&2nd train as x & y.

So, Apply the formula,

5/18(x-y)*T (T as time) = 5/18(46-36)*36.

= 50*36/18.

= 100.

So, we have 2X = 100.

X = 100/2 = 50 m.

By using the formula, if we solve the problem in SI unit we get 49.86 as answer.

Can any one explain how the step below ?

2x /36 = 25 /9.

2x/36 = 25/9.

Please make it cross multiplication simply,
(2x*9) = 25*36),

=>18x = 900.
=>x = 900/18.
=>x = 50m.

Since we are talking about relative speed (means b/w two trains. ).

Hence taking distance also combing length of two trains.

At final we are making two train details as single train details after finding we can extract two trains details.

Trains are running in same direction so the relative speed is different.

Speed of train 1 - speed of train 2.
46 - 39 = 10 Km/hr.

Convert Km/hr to m/sec.
10* 5/18 = 5/3.

Now multiply with faster train cross time ie 36 with obtained value.
36*5/3 = 50m.

In this problem length of two train will be equal therefore L = 2X.
That is distance covered = 2X.

D = SPEED*TIME.
2X = 10*(5/18)*36.

Solve the above equation you can easily get a answer.

Let the length of each train is X.

Than total length which should be covered to pass the train = 2X.

The speed of train to pass the 2X distance = 2X/36.

The relative distance of trains = 46-36 = 10 km /hr.

So 10*(5/18) = 2X/36.

X = 50 answer.

Length of the train = X.

Equal length of 2 trains = 2X.

If same direction = u-v = (46-36)km/hr = 10km/hr.

Speed = (Distance or length)/Time.

10 km/hr = 2X/36 sec.

(10*5/18) m/sec = 2X/36 sec.

X = 50 sec answer.

(Note : if opposite direction = u+v).