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:
475 comments Page 46 of 48.
Alan. said:
5 years ago
How x-5 came?
Lakshmi said:
5 years ago
Relative speed subtracted by actual speed so we get X - 5.
Kavya said:
5 years ago
Why it is divided 125/10? Please explain.
Luci said:
5 years ago
We are finding the speed of the train.
So,
Speed = distance /time.
=> Speed = 125/10.
So,
Speed = distance /time.
=> Speed = 125/10.
Azhr said:
5 years ago
(X-5) * 5/18 = 125/10.
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.
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