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:
493 comments Page 26 of 50.
Krishna said:
1 decade ago
Is there any shortcut method to learn the relative motion?
Shashi said:
1 decade 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.
Shashi said:
1 decade 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.
Shikha said:
1 decade 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.
John said:
1 decade ago
@Swati
To convert km/h into m/sec.
To convert km/h into m/sec.
PANKAJ BARWAL said:
1 decade 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.
Vishal Motwani said:
1 decade 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.
Saggy said:
1 decade 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.
Yrs said:
1 decade ago
Both train and man move same direction then relative speed is the sum of train speed and man speed.
Nani said:
1 decade 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.
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