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 20 of 48.
Varma said:
1 decade ago
How he equated 45 to x-5?
Vashu said:
1 decade ago
What is 5/18 and where its come in?
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.
Sushma said:
1 decade ago
Why should we use x-5 here please explain once again.
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.
Sadhana said:
1 decade ago
Please explain the km/s. We should get the km/s is 5/18, but why we would get the 18/5. How is possible it is? Please explain this friends.
Rishi said:
1 decade ago
Answer must be 55, Because train has to cover 125m+distance covered by man in 10 sec which is 5*10/3600.
Vishal patel said:
1 decade ago
L = Length of a train.
S1 = Speed of train.
S2 = Speed of man.
T = Time taken by train.
*************** Here is simple formula *********************
T = L/(S1 - S2) * (18/5).
************************************************
10 = 125/(S1 - 5) * (18/5).
=> (S1 - 5) = (125/10)*18/5.
=> (S1 - 5) = (25/2)*18/5.
=> (S1 - 5) = 45.
=> S1 = 45 + 5.
Ans : S1(train's speed) = 50 km/h.
S1 = Speed of train.
S2 = Speed of man.
T = Time taken by train.
*************** Here is simple formula *********************
T = L/(S1 - S2) * (18/5).
************************************************
10 = 125/(S1 - 5) * (18/5).
=> (S1 - 5) = (125/10)*18/5.
=> (S1 - 5) = (25/2)*18/5.
=> (S1 - 5) = 45.
=> S1 = 45 + 5.
Ans : S1(train's speed) = 50 km/h.
Jasper said:
1 decade ago
How it is saying that relative speed of the train is 45?
Its only the speed of the train, can anyone tell me?
Its only the speed of the train, can anyone tell me?
Munna raj said:
1 decade ago
Let me explain about converting km/hr into m/s in detail.
1 km = 1000 meters.
1 hr = 3600 seconds.
1 km/hr = 1000/3600 m/s.
= 10/36 m/s.
= 5/18 m/s.
Therefore 1 km/hr = 5/18 m/sec.
1 km = 1000 meters.
1 hr = 3600 seconds.
1 km/hr = 1000/3600 m/s.
= 10/36 m/s.
= 5/18 m/s.
Therefore 1 km/hr = 5/18 m/sec.
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