Aptitude - Problems on Trains - Discussion

Train passes 36 sec.
Man standing 20 sec.
Train speed = 54 km/h.
platform length = ?

Train length = (54*5/18) * 36.
= 30/2 * 36.
= 30 * 18.
Train length = 540.

Platform length = (54*5/18) * 20.
= 30/2 * 20.
= 30 * 10.
= 300.

Platform length = 540 - 300.
= 240=> Ans.

Given the speed of the train is 54 km/hr.

In 60*60second.
15m in 1 seconds.
90m in 6 seconds.
150m in 10 seconds.
240m in 16 seconds.

Because the time diff is 16 seconds Platform length.

Velocity of train v = 54km/h = 15m/s

We have a train passing 2 things, a man and a platform. Consider these to be two seperate instances.

i.e Use the velocity eqn individually for both cases :
1) For Platform:
We know v = s / t (v : velocity, s : distance, t : time)
v = 15m/s
s = l + x (l is length of train and x is length of platform)
t = 36s for passing platform
So we substitute and get the eqn :
15 = (l+x)/36
We want to find the platform length, i. e x.

2)For the man:
v = 15m/s
s = l (length of train)
t = 20s for passing man.

We get :
15 = l / 20.
Solving for l we get, l = 300m.

Subbing l into the platform eqn earlier we get:
15 = (300 + x)/36
540 = 300 + x (15 x 36 = 540)
x = 540-300 = 240m.
Bish Bash Bosh, there's the length of the platform : 240m.

Speed=54*5/18=15m/s.
Distance = 36 - 20s = 16,
=>15*16=240m.

1) First calculate the train distance.

D = S×T.
S = 54×5/18,
S = 15m/s,
D = 15×20 = 300m.

2) Calculate the platform + train distance.
D = 36×15
= 540m
Platform distance
540 - 300 = 240m.

Given,

Whole time spent on the platform as and assume it as t1 = 36 sec.
A man standing on the platform assumes it as t2 =20 sec.
We need the length of the platform.
Time (t1-t2) = 36 - 20 = 16sec.
Speed = 54 km/hr.
Convert km/hr to m/s.
1 km/hr = 1 * 5/18 m/s.
54 *5/18 = 3 * 5 = 15.
Length or distance of platform =speed * time.
=15 * 16 = 240m.

Speed = l + b (length of train +platforn).
Speed of train = 54*5/18 = 15.
speed = d/t -----> d = s*t.
d = 15*36-20 (time of train - time of man).
d = 240m.

@All.

Here is the explanation:

Train speed is 54 km/h.

(Sum of the seconds taken for cross = 36 - 20 =16 sec.

If we know how many meters crossed in 1 sec we can find how long that travelled in 16 sec)
The train can cross 54 km per 1 hour.
54km =5400m (because we need ans in m)
1 hour = 60mnts and 60 sec total 3600 sec.

Check the unit mentioned km/h.
We have 54000 for km and 3600 for hour.
Substitute this in km/h.
54000/3600 = 540/36 = 180/12.
= 90/6 = 15.

So, the train can cross 15m per sec;
So it takes 1 sec for 15m.
Then it takes 16 sec to cross.
15 * 16 = 240 m.
So, the train crossed 240 m length of the platform.

54×5/18x(36 sec-20 sec).
= 15 × 16 = 240.

Speed = 15mtr/hr.
15*20 = 15 * 36,
300 = 540.
= 540 - 300.
Length = 240.