Aptitude - Problems on Trains - Discussion

Can any one explain me, if suppose

l-------------------m------------l
A                   B            C
l--------20S--------l------16S---l
l---------------36s--------------l

Train is takin 20s to pass the man and then 16s to pass the remaining platfom so it comes to 36s
and the speed for train is 15m/s
according to this it shoulb be 15*36= 540m
300m the point man is standing on platform and 240m for the remaining platform

Therefore 300m+240m=540m the total lenght of platform.

First we are calculate the length of train compared with a man standing on the platform.

= (15*20) m.

=300m.

Second we are calculate the length of train compared with they passes a station platform.

= (15*36) m.

=540m.

We wanted to the length of platform X.

So, the length of platform X and the length of train compared with a man standing on the platform equal to the length of the train compared with they passes a station platform.

X+300m=540m.

X= (540-300) m.

=240m.

We were got the length of platform 240m.

I solved in my own knowledge.

./...................

(think "....." it is a platform and a man"/" standing at the very beginning of the platform).

The train passes the station platform in 36 sec and passes the man"/" standing on the platform in 20 sec.

The length of the platform including the man is= 36*15=540 m.
And the length of the man including platform is=20*15=300 m.

So, the length of exact platform=540-300=240 m.

Train crossing station platform in 36 sec with speed of 54km/hr. Question asked what is the length of platform?

54 x 1000 /3600 = 15m/sec train travel distance.

So for 36 sec train is crossing the platform.

Total length of the platform is 36 x 15 = 540mts.

If question asked what is the length of train then we have to calculate 20 sec X 15 m /sec = 300 mts.

If asked what is the balance length of platform from man standing place, then (36-20= 16) 16 x 15 =240mts.

I hope my view is correct.

According to my understanding,

1- In 36s train passes the total length which is unknown.
2- In 20s train passes the man which will be our reference point to calculate the speed.

So, from formula: Length or Distance = Time * Speed.

Length of train = 20s * 54(1000/60 * 60).
Length of train = 300 m.

Total length (Platform & train) = 36s * 54(1000/60 * 60).
Total length (Platform & train) = 540m.

Platform length = Total length = Train length = 540 -300 = 240m.

We know that,
s = d*t.

The train has a speed of 54 km/hr.

i.e 54(5/18) = 15 m/sec.
Total distance is sum of train dist and platform distance.

Here we should consider one thing i.e a man is standing 20 sec in plat form during the train crosses the platform. Hence that will gives the length of train So the train length is,
15*20=300 m(s=d*t).

Total distance 300+x ;x is the dist of platform.

Total time 36 sec. So,
300+x/36 = 15.
Finally x = 240 meters.

@Abhishek here we are supposed to find the length of the platform.
once we find the speed of train that is 15msec.
length or distance=speed * time
so length of train = speed of train is 15m/s multiplied by the train taking time to cross the man's position in 20secs.
so= 15 * 20

If u calculate in this way ,then as per the mathematics , u will come to know where the man is standing....


In such cases Solve as per the formulas.
Hope u got it :)

Consider the man standing starting edge of platform. The train passes him in 20 sec means, we can measure the length of the train.

So, length of the train is,
(54km/3600sec)*20sec=300m.

Now train passed him,
Train =============>
Platform ########
Man $

From the above graph, 300m length train crossed him in 20 sec. Remaining 16sec train takes to cross the platform.
So,
Length of the platform is,
(300m/20sec)*16sec=240m.

As the man is not moving and he can be ignored as a little particle because he has not such a big length (his standing distance) as a pillar.

So if we take the time of the train passes the man, we can get the exactly length of the train.

So there, the length of the train= (15*20).

If the man would have moving, there we can't take the same length.

We are not taking the time of the platform because it has a big length which can't be ignored.

Since the train is moving toward the man you can do 36-20 seconds = 16 seconds.
Logically if u think whenever u stand on a platform and train is coming towards you the the speed of a man becomes lesser than the speed of a train.

there for distance = speed x time = (54 x 1000 meters/ 3600 seconds).x 16 sec
= 15 x 16
= 240 meters