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.
Mounika said:
1 decade ago
What 50/3 I didn't understand this step?
Mancy said:
1 decade ago
@Mounika.
We supposed the speed of the first train = x.
Nd speed of the faster train which is moving twice as fast the other = 2x (as we have given).
Now, given length of each train = 100m,
Time = 8sec,
Substitute these value in formula.
Time = (distance/speed).
8sec = (100+100/x+2x).
"Here we are adding the values b'coz the trains are in opposite direction with each other, which you can easily understand by reading the formula column. ".
8 = 200m/3x.
By cross multiplication.
24x sec = 200m.
x = 200/24.
x = 25/3 m/sec.
When we convert it into km/hr it becomes.
x = 30km/hr but.
Acc. To question they are asking for faster train which is 2x.
So by putting the value of x in 2x we'll get the correct answer.
2(30km/hr).
Answer = 60 km/hr.
We supposed the speed of the first train = x.
Nd speed of the faster train which is moving twice as fast the other = 2x (as we have given).
Now, given length of each train = 100m,
Time = 8sec,
Substitute these value in formula.
Time = (distance/speed).
8sec = (100+100/x+2x).
"Here we are adding the values b'coz the trains are in opposite direction with each other, which you can easily understand by reading the formula column. ".
8 = 200m/3x.
By cross multiplication.
24x sec = 200m.
x = 200/24.
x = 25/3 m/sec.
When we convert it into km/hr it becomes.
x = 30km/hr but.
Acc. To question they are asking for faster train which is 2x.
So by putting the value of x in 2x we'll get the correct answer.
2(30km/hr).
Answer = 60 km/hr.
(1)
Studybeforexam said:
1 decade ago
25/3 + 25/3 = 50/3 i.e. 3 being a common denominator.
Sudha said:
1 decade ago
I did not understand how you got 50/3? Please I need a clear explanation.
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)
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.
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.
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.
Khumalo said:
1 decade ago
Where is 3 coming from?
Srinu said:
10 years ago
What is formula distance?
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