Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 29)
29.
A train travelling at 48 kmph completely crosses another train having half its length and travelling in opposite direction at 42 kmph, in 12 seconds. It also passes a railway platform in 45 seconds. The length of the platform is
Answer: Option
Explanation:
Let the length of the first train be x metres.
| Then, the length of the second train is |  |
x |  |
metres. |
| 2 |
| Relative speed = (48 + 42) kmph = | |
90 x | 5 | |
m/sec = 25 m/sec. |
| 18 |
 |
[x + (x/2)] | = 12 or | 3x | = 300 or x = 200. |
| 25 | 2 |
Length of first train = 200 m.
Let the length of platform be y metres.
| Speed of the first train = | |
48 x | 5 | |
m/sec = | 40 | m/sec. |
| 18 | 3 |
| (200 + y) x |
3 | = 45 |
| 40 |
600 + 3y = 1800
y = 400 m.
Discussion:
48 comments Page 4 of 5.
Borshon said:
8 years ago
Opposite direction,so speed of 2 train= 48+42=90, so length of 2 trains is =90*12*5/18=300. Given that 2nd train is half of the first train, so the length of first train= 200 m.
Now, length of platform =(200+x)18/48 * 5 = 45.
Solving, x = 400 m.
Now, length of platform =(200+x)18/48 * 5 = 45.
Solving, x = 400 m.
Reka said:
8 years ago
Can anybody tell me why they have taken the 1st train to calculate the length of the platform, why not both the trains.
Umang said:
8 years ago
@Reka.
Here in this question condition is given that only first train cross the railway platform in 45 seconds.
Here in this question condition is given that only first train cross the railway platform in 45 seconds.
Suyash said:
7 years ago
Can anyone help me to get this step?
X+(x/2)/25=12==> 3X/2 =300 ==> X=200.
X+(x/2)/25=12==> 3X/2 =300 ==> X=200.
Chandan.b said:
7 years ago
Can anybody explain this step for me?
x + (x/2)] = 12 or
3x = 300
or x = 200.
Therefore Length of first train = 200 m.
x + (x/2)] = 12 or
3x = 300
or x = 200.
Therefore Length of first train = 200 m.
Sai said:
7 years ago
Can anyone explain me in simple way?
Shivani said:
7 years ago
As per knowledge, it is 200m.
Riya said:
7 years ago
Can anybody help me?
Why we are taking the first train speed for calculating the length of the platform?
Why we are taking the first train speed for calculating the length of the platform?
Sayli said:
7 years ago
@Riya.
In the question it is mentioned that first train completely passes the second train and also passe the platform that's why we have to consider the first trains speed.
For that first we have to calculate the first train.
In the question it is mentioned that first train completely passes the second train and also passe the platform that's why we have to consider the first trains speed.
For that first we have to calculate the first train.
Sunny Talukdar said:
6 years ago
@Sai.
RS=(48+42)=90kmh
Then 90*5/18=25m/s.
So, First Train + 2nd Train Total Length = 25m/s * 12second = 300M.
ATQ,
First Train = 200M.
2Nd Train = 100M.
Now,
First Train Speed in Ms = 48 * 5/18 = 40/3.
So, First train+platform Total Length = 40/3 * 45 = 600M.
So, platform length is =600M-200M = 400M.
@Reka.
We use first train Speed because it's moving towards the platform and more important For ATQ we use First train speed we can't use both the speed because 2nd train is moving opposite.
RS=(48+42)=90kmh
Then 90*5/18=25m/s.
So, First Train + 2nd Train Total Length = 25m/s * 12second = 300M.
ATQ,
First Train = 200M.
2Nd Train = 100M.
Now,
First Train Speed in Ms = 48 * 5/18 = 40/3.
So, First train+platform Total Length = 40/3 * 45 = 600M.
So, platform length is =600M-200M = 400M.
@Reka.
We use first train Speed because it's moving towards the platform and more important For ATQ we use First train speed we can't use both the speed because 2nd train is moving opposite.
(7)
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