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 23 of 49.
Ayushi said:
10 years ago
Why x - 5? Not as 5- x?
Nani said:
10 years ago
Thank you friends, now I get clarity.
I am thinking speed is 45kmph and boy running speed is 5kmph so same direction we need to subtract the speed so I got 40kmph. But now I clarified we got 45kmph is already subtracted with 5kmph so now we need to find train speed so we must add 5kmph to 45kmph 50kmph is ams.
I am thinking speed is 45kmph and boy running speed is 5kmph so same direction we need to subtract the speed so I got 40kmph. But now I clarified we got 45kmph is already subtracted with 5kmph so now we need to find train speed so we must add 5kmph to 45kmph 50kmph is ams.
Yrs said:
10 years ago
Both train and man move same direction then relative speed is the sum of train speed and man speed.
Saggy said:
10 years ago
Man is moving in same direction of train if man stop them train will less time to cross him but man is walking in same direction therefor man speed will be add in train speed if man walking in opposite direction of train then it minus from that.
Vishal Motwani said:
10 years ago
Important points to remember:
The Relative speed when two movable things whose speeds x, y are moving in the same direction is = x - y.
The Relative speed when two movable things whose speeds x, y are moving in OPPOSITE direction is =x + y.
The Relative speed when two movable things whose speeds x, y are moving in the same direction is = x - y.
The Relative speed when two movable things whose speeds x, y are moving in OPPOSITE direction is =x + y.
PANKAJ BARWAL said:
10 years ago
@John.
To convert km/h into m/sec we multiply speed by 5/18.
Because 1km = 1000m &1hour = 3600 sec.
Therefore 1000/3600 = 5/18.
And also for convert m/sec into km/h we multiply speed by 18/5.
3600/1000 = 18/5.
To convert km/h into m/sec we multiply speed by 5/18.
Because 1km = 1000m &1hour = 3600 sec.
Therefore 1000/3600 = 5/18.
And also for convert m/sec into km/h we multiply speed by 18/5.
3600/1000 = 18/5.
John said:
10 years ago
@Swati
To convert km/h into m/sec.
To convert km/h into m/sec.
Shikha said:
10 years ago
Why did we take relative speed twice ?
Once with the main i.e 125/10 * 18/5 then again, x- 5.
Please clarify my doubt.
Once with the main i.e 125/10 * 18/5 then again, x- 5.
Please clarify my doubt.
Shashi said:
10 years ago
@Krishna.
The thought of shortcut methods comes when we are not able to understand the problem. My word is understanding a problem clearly is itself a shortcut.
The thought of shortcut methods comes when we are not able to understand the problem. My word is understanding a problem clearly is itself a shortcut.
Shashi said:
10 years ago
@Suma
Relative speed comes when we measure speed between any objects moving at a time.
Here man and train are moving at a time.
Relative speed comes when we measure speed between any objects moving at a time.
Here man and train are moving at a time.
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