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 39 of 50.
Sathish Chandran said:
9 years ago
May I know why we multiply the speed by 18/5?
Sivalaxman said:
9 years ago
They are two formulas for this,
1. X mts/sec = X*18/5 km/hr,
2. X km/hr = X*5/18mts/sec,
When you see the question the options are given in km/hr then we 1. Formula for this solution.
1. X mts/sec = X*18/5 km/hr,
2. X km/hr = X*5/18mts/sec,
When you see the question the options are given in km/hr then we 1. Formula for this solution.
Siva laxman said:
9 years ago
The relatie speed of the train = if opp direction = s1+s2.
Same direction s1~s2.
Same direction s1~s2.
Rony shaha said:
9 years ago
Speed*time=distance or pole's length,
How I can calculate length of train?
How I can calculate length of train?
Chandrasekar said:
9 years ago
Why using 18/5?
Please explain.
Please explain.
Bala said:
9 years ago
Why are you divided 125/10 at the 1st step? Please explain.
ASHWINI said:
9 years ago
Thank to all the given explanation.
Jeevitha said:
9 years ago
Here 18/5 used. Because to convert 125m to km/hr from km/hr to m/sec multiply by 5/18.
Jeevitha said:
9 years ago
Somebody asking that why x-5 here. Note that the man running in the same direction. So we have to subtract. If it is opp we have to add. Because man beats train spd. So man power should be subtracted. Then only we can get an exact speed of the train.
Shreya Parmar said:
9 years ago
Using [a+b] / [u-v] = t.
a = size of train = 125
b = size of man = 0
u = speed of train = ?
v = speed of man = 5km/hr =5*5/18 = 25/18 m/s
t = time by which train crosses the man =10 sec
substitute the values in the formula we have,
[125-0]/[u- 25/18] = 10
further solving we get
250/18 =u; which is in m/s
now convert it into km/h by multiplying LHS with 18/5
we have u =50km/h
which is the right answer.
a = size of train = 125
b = size of man = 0
u = speed of train = ?
v = speed of man = 5km/hr =5*5/18 = 25/18 m/s
t = time by which train crosses the man =10 sec
substitute the values in the formula we have,
[125-0]/[u- 25/18] = 10
further solving we get
250/18 =u; which is in m/s
now convert it into km/h by multiplying LHS with 18/5
we have u =50km/h
which is the right answer.
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