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:
487 comments Page 1 of 49.
Surya said:
3 weeks ago
Given man's speed = 5km per hour.
The train length is 125m.
The train crosses man in 10 seconds.
It means both the train and the man are moving in the same direction.
The speed related to man is 125m/10sec, which is 12.5m/s.
{convert this into km/hr:- [basic idea:-km/hr to m/s or viceversa;
we know that:1km=1000m, 1hr = 3600sec,
1km/hr to m/s:-1000/3600 = 5/18m/s.
For n*km/hr to m/s = n * (5/18)m/s.
And for viceversa(m/s to km/hr) :n*(18/5)km/hr}.
Now, convert 12.5m/s into km/hr:-12.5*18/5 = 45km/hr.
This is nothing but relative speed, according to man, is 45km/hr.
In basic;
Relative speed = |speed of object1 - speed of object2|(if in the same direction).
Relative speed = |speed of object1 + speed of object2|(if in opposite direction).
The problem is in the same direction,
So;
45 = speed of train - speed of man.
Therefore, the speed of the train = 45 + 5 = 50km/hr.
The train length is 125m.
The train crosses man in 10 seconds.
It means both the train and the man are moving in the same direction.
The speed related to man is 125m/10sec, which is 12.5m/s.
{convert this into km/hr:- [basic idea:-km/hr to m/s or viceversa;
we know that:1km=1000m, 1hr = 3600sec,
1km/hr to m/s:-1000/3600 = 5/18m/s.
For n*km/hr to m/s = n * (5/18)m/s.
And for viceversa(m/s to km/hr) :n*(18/5)km/hr}.
Now, convert 12.5m/s into km/hr:-12.5*18/5 = 45km/hr.
This is nothing but relative speed, according to man, is 45km/hr.
In basic;
Relative speed = |speed of object1 - speed of object2|(if in the same direction).
Relative speed = |speed of object1 + speed of object2|(if in opposite direction).
The problem is in the same direction,
So;
45 = speed of train - speed of man.
Therefore, the speed of the train = 45 + 5 = 50km/hr.
(8)
Supriyo Das said:
2 months ago
@Kiran.
There is x - 5 = 45 which means x = 45 + 5.
So, the result will be 50.
There is x - 5 = 45 which means x = 45 + 5.
So, the result will be 50.
(2)
Harshitha m said:
2 months ago
Can you explain in detail?
(2)
Menaka said:
2 months ago
Why commonly mention that 5/18? Please explain.
(9)
Kiran said:
2 months ago
@Naveen reddy.
Why adding +5? please explain to me.
Why adding +5? please explain to me.
(7)
Manikandan said:
3 months ago
Explain the answer.
(1)
Jayaprakash said:
3 months ago
How 13.89 came? Please explain to me.
(4)
Nether said:
3 months ago
It's 50 meters/second.
(1)
Nig said:
4 months ago
Thanks all for explaining it.
(3)
Joy said:
7 months ago
Here;
1 km = 1000m.
1 hour = 3600 seconds,
Then you change the Km/hr to m/sec.
= 1000/3600.
= 5/18 m/second.
1 km = 1000m.
1 hour = 3600 seconds,
Then you change the Km/hr to m/sec.
= 1000/3600.
= 5/18 m/second.
(66)
Post your comments here:
Quick links
Quantitative Aptitude
Verbal (English)
Reasoning
Programming
Interview
Placement Papers