Aptitude - Problems on Trains - Discussion

I'll explain you @Sakshi that why we are adding with the distance travelled.

Suppose the train passes through a pole or a stationary man we consider only length of the train as a distance travelled because length of man or pole is negligible but when we come across the platform well have to consider the length of platform also as a distance travelled because the train passes the platform in the given time so lengthy of platform is also added with the length of train.

Here they given train speed=72kmph now convert into m/s that is 72*5/18=20m/s.

And time 26sec given. This time taken by the train to cross the total platform.

So now we know train speed, and time. Speed=distance/time.

Distance=speed*time=20*26=520m.

So this is total distance of platform and train. i.e (platform+train length).

Platform+Train length=520.

250+Train length=520.

Train length=520-250=270m.

Shortcut:

Speed of the train is 20 m/sec.

Therefore for 1 sec--20 m.

For 26 sec -- ?

20*26=520/1.

It means for 26 sec train crosses 520m. It includes length of train also, therefore we need minus the length of the train to get the length of the platform.

i.e., 520-250 = 270.

@Avn.

The total distance covered by train in order to cross the platform will be only x+250.

This is because the length of platform is given, we only have to find out the length of train. So that's why there will be only one x.

I hope you get it.

Distance = speed * Time.
So Distance = X+250.
Where x= Length of train.

Speed = 72*5/18 m/s (Conversion from km/s to m/s).
i.e., 20 m/s.

And time = 26 seconds.
Therefore X+250 = 20 * 26.
X = 520-250.
X = 270 m.

First convert 72km/hr in m/sec
So, 72/1*1000/3600
=72*5/18
=20m/sec.

D = s * t
= 20*26
= 520.

Its a distance of Train + platform; this is because full length of train pass full length of platform.

So,
520-250=270.

@Sonia.

Here relative speed in sense where two forces come in opposite directions and in turn of collide force.

In above said question the trans come in same direction so it is added if it in opposite direction it is subtracted.

@All.

Why 72 is multiplied by 5/18?

Ans: Because of unit conversion.....

72 is in kmph and our answer is in the meter so it is required to convert speed from kmph to mph.

I hope, this will help you all.

Hi sonam,
Let me explain about converting km/hr into m/s in detail.

1 km = 1000 meters.
1 hr = 3600 seconds.

1 km/hr = 1000/3600 m/s

= 10/36 m/s

= 5/18 m/s.

Therefore 1 km/hr = 5/18 m/sec.

Use this Formula for all train problems.

Train length + object length * hr * 60m * 60se/speed(1000).

26= T+250 * 60 * 60/72000,
250+ 26 * 72000/60 * 60,
520 - 250 = 270.