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 8 of 48.
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.
Azhr said:
5 years ago
(X-5) * 5/18 = 125/10.
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.
Kavya said:
5 years ago
Why it is divided 125/10? Please explain.
Lakshmi said:
5 years ago
Relative speed subtracted by actual speed so we get X - 5.
Alan. said:
5 years ago
How x-5 came?
PKP said:
5 years ago
Wrong solution.
Man also traveled a distance of 5*5/18*10=125/9 m in 10 sec. So this distance should be added to 125 m when calculating relative speed, so relative speed = (125+125/9)/10 = 125/9 m/s = 125/9 * 18/5 km/s = 50 km/hr.
So the speed of the train is 50+5 = 55 km/hr.
Man also traveled a distance of 5*5/18*10=125/9 m in 10 sec. So this distance should be added to 125 m when calculating relative speed, so relative speed = (125+125/9)/10 = 125/9 m/s = 125/9 * 18/5 km/s = 50 km/hr.
So the speed of the train is 50+5 = 55 km/hr.
Sonu said:
5 years ago
x-5 = 45.
x = 45+5(because when 5 goes from the left side to right then it will be added into 45).
So,
x = 50 Answer.
x = 45+5(because when 5 goes from the left side to right then it will be added into 45).
So,
x = 50 Answer.
Pradeep said:
6 years ago
It's 50 m/s unit.
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