Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 26)
26.
Two trains are running at 40 km/hr and 20 km/hr respectively in the same direction. Fast train completely passes a man sitting in the slower train in 5 seconds. What is the length of the fast train?
Answer: Option
Explanation:
| Relative speed = (40 - 20) km/hr = |  |
20 x | 5 |  |
m/sec = | |
50 | |
m/sec. |
| 18 | 9 |
 Length of faster train = |
|
50 | x 5 | |
m = | 250 | m = 27 | 7 | m. |
| 9 | 9 | 9 |
Discussion:
72 comments Page 2 of 8.
Ganesh said:
9 years ago
@Rohit Saluja.
When you consider relative velocity there is no need of knowing where the man is sitting and once you find out relative velocity the method of solving the problem is same as solving the problem of 'train passing a signal post or pole' so what they have given as solution is absolutely fine.
When you consider relative velocity there is no need of knowing where the man is sitting and once you find out relative velocity the method of solving the problem is same as solving the problem of 'train passing a signal post or pole' so what they have given as solution is absolutely fine.
Arun said:
1 decade ago
Hi subha... @ not like dat ma...dats in d case if d faster train crosses d slower train... But in dis case d train just crosses a man(which may be considered as a point)....
Vaishna.v said:
1 decade ago
I have cleared it in another way:
We have to calculate the length of faster train only.
The relative speed = (40-20) km/hr = 20 km/hr.
Let the length of the faster train be f.
Then, (f/20 km/hr) = 5.
20 km/hr = 20*5/18 s = 50/9 s.
(9f/50) = 5.
250/9 is the answer.
We have to calculate the length of faster train only.
The relative speed = (40-20) km/hr = 20 km/hr.
Let the length of the faster train be f.
Then, (f/20 km/hr) = 5.
20 km/hr = 20*5/18 s = 50/9 s.
(9f/50) = 5.
250/9 is the answer.
Manish said:
9 years ago
We can't find the slower train length as it will never pass the faster train.
So in order two find slower train length we need how much time the faster train take to pass the slower train not the man.
Relative means that slower is still.
So in order two find slower train length we need how much time the faster train take to pass the slower train not the man.
Relative means that slower is still.
(1)
Haritha said:
1 decade ago
Hi guys but the train crosses a man who is sitting in the train but not the one who is standing simply. Also he might be sitting in middle or some where else we have to calculate the distance from which the man is sitting. Isn't it?
Ratnesh said:
1 decade ago
Hey to convert km/hr to m/s we have to use this conversion unit,
i.e 1000/(60*60)= 1000/3600.
Here 1 km = 1000 m and 1 hr = 60*60 =3600 seconds.
And when simplified it will give 5/18.
Hope your doubt about 18 would be clear now?
i.e 1000/(60*60)= 1000/3600.
Here 1 km = 1000 m and 1 hr = 60*60 =3600 seconds.
And when simplified it will give 5/18.
Hope your doubt about 18 would be clear now?
Pratik Patil said:
7 years ago
Just consider that man is running at speed of 20 km/hr, then find the relative speed between train and man i.e. (40-20)km/hr=20km/hr=20*5/18 m/s=50/9 m/s.
The length of train (faster) = speed X time = 5*50/9 = 27 7/9 m.
The length of train (faster) = speed X time = 5*50/9 = 27 7/9 m.
Nilesh z. said:
8 years ago
Just consider that man is moving at 20 km/hr. Now solve the problem as you solved problem number 27 by considering just one man. You will come to know why we don't consider the length of the slower train.
GAURAV said:
8 years ago
How can we assume the man will be sitting on a forehead of the train? He can be sitting anywhere in the train.
I think the answer will be can't be determined until exact location of man is not mentioned.
I think the answer will be can't be determined until exact location of man is not mentioned.
Sumukh said:
6 years ago
Since the faster train is passing man sitting inside the slower train in 5 seconds. The length of slower train may be treated as man distance which is negligible just like pole. So, the right answer is C.
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