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 5 of 5.
Rani said:
1 decade ago
Why they have substituted time as 12 why not 25?
The problem is related to length of platform not the length of train.
Can any one explain this?
The problem is related to length of platform not the length of train.
Can any one explain this?
Dinesh said:
1 decade ago
Can any one explain why he took the 48 kmph in the length of the platform?
Stuti said:
1 decade ago
I didn't understand any bit of the problem. Please some one do explain in an easy way :).
Shashank said:
1 decade ago
Answer will be be 400 meter because you guys did not read question properly.
It is clearly mention mean n last line the word "it" is referred for first train.
So now you have length of first train, its time to cover platform of length y meter and its speed 45 km/hr now use simple formula.
s(48km/hr) = (length of train(200)+length of platform(y)) /time to cover/cross platform(45 sec).
So y=400 meter.
It is clearly mention mean n last line the word "it" is referred for first train.
So now you have length of first train, its time to cover platform of length y meter and its speed 45 km/hr now use simple formula.
s(48km/hr) = (length of train(200)+length of platform(y)) /time to cover/cross platform(45 sec).
So y=400 meter.
Javid Mir said:
1 decade ago
Let length of first train be 'L' therefore length of 2nd train is 'L/2'.
Now, since trains are moving in opposite direction, there relative speed is,
(48+42) km/h = (L+L/2) /12.
(48+42) x 5/18 m/sec = (3/2 L) /12.
90 x 5/18 x 12 = 3/2 L.
300 = 3/2 L => L = 300 x 2/3 => L = 200 mtrs.
Now with respect to Plateform, Let distance of Platform be 'X'.
Therefore, Total Length = 200 + X and Speed is of first train i.e. 48 Kms/hr & time = 45 secs.
48 kms/hr = 48x5/18 mtrs /sec.
Therefore, 48 x 5/8 = 200 + X/45.
(48x5x45) /18 = 200 + X => 600 = 200 + X => X = 600-200.
X = 400 mtrs.
Now, since trains are moving in opposite direction, there relative speed is,
(48+42) km/h = (L+L/2) /12.
(48+42) x 5/18 m/sec = (3/2 L) /12.
90 x 5/18 x 12 = 3/2 L.
300 = 3/2 L => L = 300 x 2/3 => L = 200 mtrs.
Now with respect to Plateform, Let distance of Platform be 'X'.
Therefore, Total Length = 200 + X and Speed is of first train i.e. 48 Kms/hr & time = 45 secs.
48 kms/hr = 48x5/18 mtrs /sec.
Therefore, 48 x 5/8 = 200 + X/45.
(48x5x45) /18 = 200 + X => 600 = 200 + X => X = 600-200.
X = 400 mtrs.
Piyush said:
1 decade ago
Correct Answer is 200m.
Two cross Platform Distance would be 400+y.
i.e. If train length is 200 than it should be 400+y.
Two cross Platform Distance would be 400+y.
i.e. If train length is 200 than it should be 400+y.
Sonu said:
1 decade ago
Can any one explain why should we consider second train length as "x/2"?
Sumit said:
10 years ago
Read the question carefully.
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