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:
476 comments Page 15 of 48.
Challu said:
1 decade ago
Think you are in a train, another one moving side by you in parallel, what will you experience? the train is in less speed of actualone. To find original speed you have to add your train speed.
Chithra said:
8 years ago
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.
Similarly, the reciprocal of m/sec is used to calculate km/hr.
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.
Similarly, the reciprocal of m/sec is used to calculate km/hr.
Plabon said:
1 decade ago
Let the speed of train= x km/hr.
So relativee speed = distance/time.
Relative speed of train = (x- 5) km/hr.
x-5 = 0.125/10/3600.
So x- 5 = 0.125x3600/10 = 45.
x = 45+5 = 50 km/hr answer.
So relativee speed = distance/time.
Relative speed of train = (x- 5) km/hr.
x-5 = 0.125/10/3600.
So x- 5 = 0.125x3600/10 = 45.
x = 45+5 = 50 km/hr answer.
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.
Mounish said:
9 years ago
Distance = speed * time.
Speed = distance/time.
Speed = (x - 5)km/hr == (x - 5) * 5/18 m/sec.
Distance = 125 m.
Time = 10 sec.
(x - 5) * 5/18 = 125/10.
x - 5 = 125/10 * 18/5.
x - 5 = 45.
Speed = distance/time.
Speed = (x - 5)km/hr == (x - 5) * 5/18 m/sec.
Distance = 125 m.
Time = 10 sec.
(x - 5) * 5/18 = 125/10.
x - 5 = 125/10 * 18/5.
x - 5 = 45.
Paras said:
8 years ago
Hers, x is supposed as speed of train. 5 is substracted because it is relative. Both are going in same direction. If the direction was supposed to be opposite then 5 should have been added.
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.
Navi said:
1 decade ago
Hi @Swati look here let me explain:
L = Speed*time.
And,
Speed = length/time.
Length = 25/2.
Time = 5/18.
And,
25/2/5/18 = 25/2*18/5.
9*5 = 45km/hr.
x-5 = 45.
45+5 = x.
x = 50km/hr.
L = Speed*time.
And,
Speed = length/time.
Length = 25/2.
Time = 5/18.
And,
25/2/5/18 = 25/2*18/5.
9*5 = 45km/hr.
x-5 = 45.
45+5 = x.
x = 50km/hr.
Sivalaxman said:
8 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.
Ravi said:
1 decade ago
It is given that
Speed of man=5km/hr
Distance travelled by man in 10s=125/9m
Distance travelled by train in 10s= {125+(125/9)}m
Hence
Speed of train = [{125+(125/9)/10]*3600 = 50 km/hr
Speed of man=5km/hr
Distance travelled by man in 10s=125/9m
Distance travelled by train in 10s= {125+(125/9)}m
Hence
Speed of train = [{125+(125/9)/10]*3600 = 50 km/hr
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