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 32 of 48.
Vishal Motwani said:
9 years ago
Important points to remember:
The Relative speed when two movable things whose speeds x, y are moving in the same direction is = x - y.
The Relative speed when two movable things whose speeds x, y are moving in OPPOSITE direction is =x + y.
The Relative speed when two movable things whose speeds x, y are moving in the same direction is = x - y.
The Relative speed when two movable things whose speeds x, y are moving in OPPOSITE direction is =x + y.
Saggy said:
9 years ago
Man is moving in same direction of train if man stop them train will less time to cross him but man is walking in same direction therefor man speed will be add in train speed if man walking in opposite direction of train then it minus from that.
Yrs said:
9 years ago
Both train and man move same direction then relative speed is the sum of train speed and man speed.
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.
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?
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.
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.
Jaydev ramnath said:
9 years ago
Why it is 18/5? Please explain.
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