Aptitude - Problems on Trains - Discussion

HI All,

Let's simplify this:

Distance traveled(d) = speed(d) * time(t) taken to travel that distance(d)

Speed is 45km/h.
Since answer needs to be in meter, let's convert Km/h into m/sec.

so, 45*(1000/3600), because 1km=1000mtr and 1hr= 3600sec(60minutes*60 sec per minute).

So, our m/sec speed(s) comes to be 45*(5/18)=25/2mtr per sec.
We have s = 25/2m/sec and t= 30 secs. so d = s*t =375mtr.

Since train itself is 130mtr long it wouldn't travel all 375mtr. So, the distance actually traveled(bridge length)by train is 375mtr- 130mtr = 245mtr.

hope this helps.

Hi coolburn its nice explanation

Is 45 km/hr relative speed between the bridge and the train?

First of all arragne them in D= ST.
S = D/T or T = D/S.

This problem is very easy to solve
speed(v) of train=45km/hr
length of train(d)=130m
time(t)=30sec
d=v*t
d=(45*5/18)*30
d=(25/2)*30
d=375
length of bridge(x)=d-length of train
x=375-130
x=245m

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).