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 29 of 48.
Hunt said:
1 decade ago
Relative velocity of train with respect to a fixed point (Let assume a pole).
v = u-5 [u is the velocity of train & 5 is of man & in same direction so negative sign].
Now by simple equation.
Length = Speed x Time.
125 = (u-5*5/18)10.
So u = 250/18 m/s = 50 km/h.
v = u-5 [u is the velocity of train & 5 is of man & in same direction so negative sign].
Now by simple equation.
Length = Speed x Time.
125 = (u-5*5/18)10.
So u = 250/18 m/s = 50 km/h.
Sushma said:
1 decade ago
Why should we use x-5 here please explain once again.
Raja said:
1 decade ago
18/5 is to convert m/s to km/hr.
5/18 is to convert km/hr to m/sec.
1 km = 1000 m
1 hr = 3600 s.
M = 1 km/1000
s =1 hr/3600.
M/s = (3600/1000) km/hr.
= (5/18) km/hr.
------------------------------------------------.
Km/hr = (1000/3600) m/s.
= (5/18) m/s.
5/18 is to convert km/hr to m/sec.
1 km = 1000 m
1 hr = 3600 s.
M = 1 km/1000
s =1 hr/3600.
M/s = (3600/1000) km/hr.
= (5/18) km/hr.
------------------------------------------------.
Km/hr = (1000/3600) m/s.
= (5/18) m/s.
Vashu said:
1 decade ago
What is 5/18 and where its come in?
Varma said:
1 decade ago
How he equated 45 to x-5?
Ravindra said:
1 decade ago
X-5 = 45 is right because train and man same side. In same side it is correct.
Nikhil said:
1 decade ago
We have added the 5 km/hr to the final answer because the speed that comes out is with respect to man and to calculate the actual speed of the train we have added 5 km/hr to the final answer.
Mohit kumar said:
1 decade ago
1 km = 1000 m/1 hr = 3600 sec = 5/18 but we want to convert just opposite.
So numerator and denominator will be interchange.
So numerator and denominator will be interchange.
Prammeela.t said:
1 decade ago
Why we relate the speed of man and train length?
Sravani said:
1 decade ago
Why relative speed? They asked only speed?
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