Aptitude - Problems on Trains - Discussion

45km In 1 hr.
45km In 60 min.
45 km In 60*60 seconds
45000m In 60*60 seconds
45000/120 In 30 seconds
375.m in 30 seconds.
375m including with train length so the train length is;
375 - 130 = 245 m ANS.

Solution:

45 * 5/18 = 12.5,
12.5 * 30 = 375,
375 - 130 = 245,
So, this is how we get 245.

My Question is why we should convert 45 km/hr into meters/per second which is a unit of speed instead of that we can convert 130/30 which is also equal to speed?

Anyone, explain this to me.

To find the length of the bridge, we need to calculate the distance the train travels in 30 seconds.

First, we convert the train's speed from km/hr to m/s:

Speed in m/s = (Speed in km/hr * 1000)/3600
So, the train's speed in m/s = (45 km/hr * 1000)/3600 = 12.5 m/s.

Now we can calculate the distance the train travels in 30 seconds:
Distance = Speed * Time.

Distance = 12.5 m/s * 30 s = 375 meters.

Since the train is 130 meters long, the remaining distance must be the length of the bridge:
Length of the bridge = Distance - Length of the train.

Length of the bridge = 375 m - 130 m = 245 meters.

Therefore, the length of the bridge is 245 meters.

Length of bridge = (speed of the train * time taken to cross the bridge) - length of the train.
= ((45*5/18)*30) - 130,
=((25/2) * 30) -130,
=(750/2) - 130,
= 375m/s - 130s,
= 245m.

@Rajesh.

We take 5/18 to convert from km/h into m/s.

l = ?
Train length =130m
Speed = 45km/hr
Time = 30s.

30s = time(130+l(m)).
30s = (130+l)m/45km/hr.
30s = (130+l)m/45 * 5/18m/s.
30s = 130+l/(25/2)m/s.

30s = (130+l) * 2/25.
30 * 25 = (130 +l)* 2.
15*25 = 130 + l.
375 - 130 = l.
245m = l.

Length of train = 130m
Length of bridge = ?
1hr = 3600sec
= 3600/30
= 120.

1km = 1000m
= 45000/120
= 375m
The length of the train is less total.
375-130 = 245.

Convert speed from km/hr to m/sec(km/hr=5/18 m/s).
Then,as we know DISTANCE=SPEED *TIME.
D = [45 * (5/18)] * 30 sec.

Then, D = 375m(This is the total distance)
So, we can subtract the total distance from the length of the train),
The length of the train is = 375 - 130 = 245m.

Length of train 130, speed 45 km/hr it crosses the bridge in 30 seconds.
What is the length of the bridge?
45km = 45000 m
1hr = 3600 s.

So
45000/3600 = 12.5 m/s
the train crosses a bridge in 30 sec then
12.5 * 30 = 375
The train travelled 375 in 30 sec.
Then distance - train length = bridge length.
375 - 130 =245.
bridge length = 245.