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:
478 comments Page 22 of 48.
Sathiyaraj said:
9 years ago
Since train and man run in the same direction,
So, in 10 seconds, train crosees 125 mts (train length) + 125/9 mts,
(5 km/hr => 5000/3600, 10 seconds => 125/9),
So train speed , 36(125 + 125/9) (10 seconds x 36 => 3600 seconds => 1 hr),
Answer : 50, 000 mts = 3600 secs => 50 km/hr.
So, in 10 seconds, train crosees 125 mts (train length) + 125/9 mts,
(5 km/hr => 5000/3600, 10 seconds => 125/9),
So train speed , 36(125 + 125/9) (10 seconds x 36 => 3600 seconds => 1 hr),
Answer : 50, 000 mts = 3600 secs => 50 km/hr.
Er.deepak said:
9 years ago
Man speed is 5km/hr.
So, km = 1000metrs.
Per hour = 60mintes = 3600second.
3600/1000 = 36/10 = 18/5.
Trains cross the man in 10 seconds.
Length of the train is =125m.
Relative man trains speed = 125/10 = 25/2.
So 25/2 x 18/5 = 45km/hr.
We let train speed is = x km/hr.
Relative to man turn speed = x - 5 = 45.
x = 45 + 5 = 50km/hr.
So, km = 1000metrs.
Per hour = 60mintes = 3600second.
3600/1000 = 36/10 = 18/5.
Trains cross the man in 10 seconds.
Length of the train is =125m.
Relative man trains speed = 125/10 = 25/2.
So 25/2 x 18/5 = 45km/hr.
We let train speed is = x km/hr.
Relative to man turn speed = x - 5 = 45.
x = 45 + 5 = 50km/hr.
Jaydev ramnath said:
9 years ago
Why it is 18/5? Please explain.
Mubarak said:
9 years ago
Thank you guys for your best explanations really easily understandable, for the non maths learners. You people are doing good, good things never stop. Please keep on posting.
Pramod.M said:
9 years ago
Length(Distance) of the train 125m, time is 10 sec. The speed of man is 5 km/hr.
Speed = D/T i.e. 125/10 = 25/2m/s.
Therefore speed in km = 25/2 * 18/5 we got 45km/hr.
Moving in the same direction we must subtract i.e. 45 - 5 = 40 km/hr.
If the man moves against the train we must add 5km/hr to 45 km/hr.
Speed = D/T i.e. 125/10 = 25/2m/s.
Therefore speed in km = 25/2 * 18/5 we got 45km/hr.
Moving in the same direction we must subtract i.e. 45 - 5 = 40 km/hr.
If the man moves against the train we must add 5km/hr to 45 km/hr.
Shweta said:
9 years ago
A solution to this problem is so simple.
Speed of train = s1;
Speed of men = s2;
S2 = 5km/hr.
The length of train =125m.
Time =10 sec.
So, convert the time and sec i.e. m/s in km/hr.
125/10 * 18/5; //convert the m/s to km/hr formula is a * 18/5.
Formula is: s1- s2 = (L1/T).
We got the equation.
S1 - 5 = (125/10) * (18/5).
S1- 5 = 45km/hr;.
S1 = 45 + 5.
S1 = 50km/hr.
Speed of train = s1;
Speed of men = s2;
S2 = 5km/hr.
The length of train =125m.
Time =10 sec.
So, convert the time and sec i.e. m/s in km/hr.
125/10 * 18/5; //convert the m/s to km/hr formula is a * 18/5.
Formula is: s1- s2 = (L1/T).
We got the equation.
S1 - 5 = (125/10) * (18/5).
S1- 5 = 45km/hr;.
S1 = 45 + 5.
S1 = 50km/hr.
Amrit Ashu said:
9 years ago
A different approach:
We have been given the running speed of the man i.e 5km/hr converting this into m/Sec we get 1.38 m/sec.
In 10 seconds this man will cover 13.8 m. So now the total distance the train has to cover in 10 seconds is 125 meters(its own length) and 13.8 m which equals 138.8 m. Using speed, time and distance formula we get S= 138.8/10 =13.8m/sec.
Convert this into Km/h we get 49.8 which is approx. 50 km/h.
We have been given the running speed of the man i.e 5km/hr converting this into m/Sec we get 1.38 m/sec.
In 10 seconds this man will cover 13.8 m. So now the total distance the train has to cover in 10 seconds is 125 meters(its own length) and 13.8 m which equals 138.8 m. Using speed, time and distance formula we get S= 138.8/10 =13.8m/sec.
Convert this into Km/h we get 49.8 which is approx. 50 km/h.
Ayushi said:
9 years ago
Why x - 5? Not as 5- x?
Nani said:
9 years 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.
Yrs said:
9 years ago
Both train and man move same direction then relative speed is the sum of train speed and man speed.
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