Aptitude - Problems on Trains - Discussion

Here, A Train 130meter long.

Speed of train=45km/hr=45000m/3600sec=12.5m/sec.

Within 30sec that train cross distance=12.5m/sec*30sec=375m/30sec.

So,Length of Bridge=Cross distance - length of Train
=375-130=245Meters.

Therefore , The Length of Train= 245Meters.

Given:
1. Length of the train = 130 m
2. Speed of the train = 45 km/hr or (25/2) m/s
3. Time taken by the train to cross bridge = 30s

Find:
Length of the bridge = x meter

First, convert speed of the train from km/hr into m/s
So, speed of the train in m/s = [45*(5/18)] km/hr = (25/2) m/s

Now,
Distance(or length) = speed * time

But,Distance = (Length of the bridge + Length of the train) = speed * time
Distance = x + 130 = (25/2) * 30

x+130 = 375
x = 375 - 130
Length of the bridge = 245 m

Thanks Nil.

dis=len of train+bridge length(take a bridge as x)
130+x
speed=45km/hr=45*5/18=25/2
time=30sec
dis=speed*time
130+x=25/2*30
130+x=375
x=245m.

Formula is = (Length of the train + Length of the object)=(Speed of the train* Time of the object).

HEY. I have a doubt. The length of train is already covering some length of the bridge. Then why we consider both lengths separately?

Your are right sushi.

Please help why we consider both lengths separately?

If the train is crossed 130m length in 10 sec it also covered length of bridge?

Why we are again consider the bridge length?

The train is already crossed the bridge in 10 sec. So the length of the bridge also covered.

Formula :- Distance=Speed/Time

Answer's in option are given in meter, that mean we can go for 5/18 ready made formula of converting km/hr to m/sec.

* 45 x 5/18 = 12.5 (for 1 second )
* 12.5(sec) x 30(sec)given = 375
* 375-130 (given )= 245.

Easy to find no need to put x and y.

45000m/360seconds = 125 mps.

30 seconds so, crossing bridge.

30*125=375m.

Subtract the train meter : 130m.

Answer : 375-130=245m.

Best Answer could be for new person:

3600 sec me 45000 meter.

1 sec me 45000/3600 12.5 meter/sec.

30 sec me 12.5*30 = 375 meter.

Train length is 130 meter .

Bridge length will be :-375-130 = 245 meter.