Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 2)
2.
A train 125 m long passes a man, running at 5 km/hr in the same direction in which the train is going, in 10 seconds. The speed of the train is:
Answer: Option
Explanation:
| Speed of the train relative to man = |  |
125 |  m/sec |
| 10 |
| = | |
25 | m/sec. |
| 2 |
| = | |
25 | x | 18 | km/hr |
| 2 | 5 |
= 45 km/hr.
Let the speed of the train be x km/hr. Then, relative speed = (x - 5) km/hr.
x - 5 = 45 
x = 50 km/hr.
Discussion:
481 comments Page 47 of 49.
Pravin said:
5 years ago
Thank you @Chandan Azad.
Pravin said:
5 years ago
For relativity the formula is divided as two that depends upon the question.
When question has same direction:
t=(l1+l2)\(u1-v1).
when question has opposite direction ;
t=(l1+l2)\(u1+v1).
In our question we has same direction, so we going to use 1st formula:
Here,
u1 = x;
v1 = 5km\hr;
t = 10 seconds;
l1 = 125m;
l2 = 0; These are the given data's.
By substitute the data's in formula;
u1-v1 = (x-5)(5\18),
10 = 125\(x-5)(5\18),
10 (x-5) = 125(18\5),
10x-50 = 450,
10x = 450+50,
10x = 500,
x=50.
When question has same direction:
t=(l1+l2)\(u1-v1).
when question has opposite direction ;
t=(l1+l2)\(u1+v1).
In our question we has same direction, so we going to use 1st formula:
Here,
u1 = x;
v1 = 5km\hr;
t = 10 seconds;
l1 = 125m;
l2 = 0; These are the given data's.
By substitute the data's in formula;
u1-v1 = (x-5)(5\18),
10 = 125\(x-5)(5\18),
10 (x-5) = 125(18\5),
10x-50 = 450,
10x = 450+50,
10x = 500,
x=50.
Pravin said:
5 years ago
Thank you @Chandhan Azad.
Ruchitha said:
5 years ago
Why did we take x-5 for the speed? Explain it.
Naresh said:
5 years ago
Trian length/trainspeed - man speed = time.
So, 125/(x-5) * 5/18 = 10.
125 * 18/(x-5)5 = 10
X-5 = 45.
X = 50.
So, 125/(x-5) * 5/18 = 10.
125 * 18/(x-5)5 = 10
X-5 = 45.
X = 50.
Charanjeet pal said:
5 years ago
Why divide 18/5? Please explain.
Sai krishna. B said:
5 years ago
Why 60*60/1000 came here? Can you please explain?
Dinesh kumar said:
5 years ago
The speed of the train be x km/hr. Then, relative speed = (x - 5) km/hr.
Please explain it, friends.
Please explain it, friends.
Wanbok Rabon said:
5 years ago
How get 18/5?
Yash said:
5 years ago
Why they have done 125/10?
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