Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 13)
13.
Two trains, each 100 m long, moving in opposite directions, cross each other in 8 seconds. If one is moving twice as fast the other, then the speed of the faster train is:
Answer: Option
Explanation:
Let the speed of the slower train be x m/sec.
Then, speed of the faster train = 2x m/sec.
Relative speed = (x + 2x) m/sec = 3x m/sec.
 |
(100 + 100) | = 3x |
| 8 |
24x = 200
| x = |
25 | . |
| 3 |
| So, speed of the faster train = | 50 | m/sec |
| 3 |
| = |  |
50 | x | 18 |  km/hr |
| 3 | 5 |
= 60 km/hr.
Discussion:
74 comments Page 4 of 8.
Vijay arun said:
9 years ago
@Ikram.
Nice explanation.
Nice explanation.
Sam said:
9 years ago
@Aditiyabala.
Super explanation, Thank you.
Super explanation, Thank you.
Praveen Sharma said:
10 years ago
How come 3?
Answer - If speed of slow train is x km/h.
In question the speed of fast train is twice to slow train.
So speed of fast train = 2*(Speed of slow train).
So speed of fast train = 2*(x) = 2x.
If trains are moving in opposite direction then we ADD the Speed. And trains are in same direction then we sub speed.
Here train in same direction so we add the speed of both train.
So x + 2x = 3x.
Answer - If speed of slow train is x km/h.
In question the speed of fast train is twice to slow train.
So speed of fast train = 2*(Speed of slow train).
So speed of fast train = 2*(x) = 2x.
If trains are moving in opposite direction then we ADD the Speed. And trains are in same direction then we sub speed.
Here train in same direction so we add the speed of both train.
So x + 2x = 3x.
Praveen Sharma said:
10 years ago
Here (100+100)/8 = 3x.
200/8 = 3x.
25 = 3x.
So x = 25/3 m/s it is speed of slow train.
We want speed of fast train, it is 2x where x = 25/2 m/s.
So speed of fast train = 2*25/3 m/s.
So 50/3 m/s.
And we convert in km/s using 18/5.
So (50*18)/(3*5) = 900/15 = 60 km/h.
200/8 = 3x.
25 = 3x.
So x = 25/3 m/s it is speed of slow train.
We want speed of fast train, it is 2x where x = 25/2 m/s.
So speed of fast train = 2*25/3 m/s.
So 50/3 m/s.
And we convert in km/s using 18/5.
So (50*18)/(3*5) = 900/15 = 60 km/h.
(1)
Srinu said:
10 years ago
What is formula distance?
Khumalo said:
1 decade ago
Where is 3 coming from?
Shiva said:
1 decade ago
Why you are all talking always 5/18 to convert kmph into m/sec, I can't understand that logic, please explain reason behind that. Thanks in advance.
Anshul Saraf said:
1 decade ago
Here both trains will not travel the same distance of 100 m. However the sum of distance travelled by both trains will be 200.
Priyesh Jain said:
1 decade ago
"D = ST".
Total distance = 100+100 = 200 m.
Relative speed = s+2s = 3s.
T= 8 sec.
Putting these values.
200 = 3s*8.
S = 200/8*3.
S = 25/3 m/s.
Now be need to calculate speed in terms of km/h.
25/3*18/5 = 30 km/h.
Speed of slower train now speed of faster train is 60 km/h that is just double.
Total distance = 100+100 = 200 m.
Relative speed = s+2s = 3s.
T= 8 sec.
Putting these values.
200 = 3s*8.
S = 200/8*3.
S = 25/3 m/s.
Now be need to calculate speed in terms of km/h.
25/3*18/5 = 30 km/h.
Speed of slower train now speed of faster train is 60 km/h that is just double.
Sudha said:
1 decade ago
When you divide 200/24, you won't get 25/3? So I request you to explain me properly.
(1)
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