Aptitude - Problems on Trains - Discussion

We have to calculate speed.

Speed = 45*5/18=25/2 m/s.

Time is given t= 30 sec.
Let's find the length of the bridge,
Let the length of the bridge is X.

And whenever a train crosses the bridge then the total distance covered by the train is the length of the bridge it's own length (train's length).

According to the motion's 1st law distance or displacement = speed * time.
X + 130 = 25/2 * 30.
2(X + 130) =750.
2X + 260 = 750.
X = (750-260)/2= 245m.

Speed = 45*(5/18)=25/2 m/s.

Displacement = speed * time(here time is 30sec).
X + 130 = 25/2 * 30.
2(X + 130) =750.
2X + 260 = 750.
X = (750-260)/2= 245m.

How do you get 25/2? Explain, please.

Why are you people adding the bridge distance?

If in case the bridge distance is lesser than the train distance, then how it will be calculated?

4.5x 5/18 = 12.5
12.5 x 30 = 375
375 - 130 = 245 ans.

Given TD = 130m, speed = 45km/h, Time = 30sec.
And Length of the Station = x.

speed = 45*5/18 .
=225/18.
So, the speed =25/2.

know the length of the station,
x + TD = speed * Time
x + 130 = 25/2 * 30
x + 130 = 12.5 * 30
x + 130 = 375.
x = 375 - 130,
Final x = 245.
The correct answer is option C.

Soln,
L.t -130m ,s -45km/hr ,t -30 sec
L.b - ?.

Let us assume length of the bridge as x,
D = s* t.

130 (l.t) + x(l.b) = 45 km/hr * 30 sec.
130 + x =45 * 5/18 m/ sec * 30 sec.

After solving we will get,
130 + x = 375,
x = 375 -130,
x = 245 m.
So, the length of the bridge is 245 m.

Why do we take 5/18, anyone, please Explain it?

To convert kilometres per hour (km/hr) to meters per second (m/sec), we use the conversion factor of 5/18. This conversion factor is derived from the relationship between kilometres and meters, as well as hours and seconds.

Here's the breakdown of the conversion:

1 kilometer = 1000 meters.
1 hour = 3600 seconds.

To convert km/hr to m/sec, we need to cancel out the kilometres and hours units while retaining the meters and seconds units. We can do this by multiplying the value in km/hr by a conversion factor that equates to 1.

To convert kilometres to meters, we multiply by 1000 (since 1 kilometre is equal to 1000 meters). This step cancels out the kilometres unit.

To convert hours to seconds, we multiply by 3600 (since 1 hour is equal to 3600 seconds). This step cancels out the hours unit.

So, the conversion factor becomes:
(1000 meters/1 kilometer) * (1 hour/3600 seconds)

Simplifying this expression gives us:
(1000/1) * (1/3600) = 1000/3600 = 5/18.

Hence, multiplying the value in km/hr by 5/18 will convert it to m/sec.

Distance travelled by Train= length of bridge + length of the train
So, x + 130m.
Speed = 45km/hr = 45 * 5/18 = 25/2 m/s.
Distance = speed * time.
25/2 * 30,
= 245m.