Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 9)
9.
Two trains are moving in opposite directions @ 60 km/hr and 90 km/hr. Their lengths are 1.10 km and 0.9 km respectively. The time taken by the slower train to cross the faster train in seconds is:
Answer: Option
Explanation:
Relative speed = (60+ 90) km/hr
| = |  |
150 x | 5 |  m/sec |
| 18 |
| = | |
125 | m/sec. |
| 3 |
Distance covered = (1.10 + 0.9) km = 2 km = 2000 m.
| Required time = | |
2000 x | 3 | sec = 48 sec. |
| 125 |
Discussion:
107 comments Page 7 of 11.
Agasthya Rana said:
1 decade ago
Why are we adding speed?
Sateesh Vudum said:
1 decade ago
For every problem like this you should find relative speed to get solution.
Need of relative speed: we can desire the solution without forming the relation between two quantities either speed or time.
Time = (L1+L2)/(relative speed);
L1-Length of train-1.
L2-Length of train-2.
Need of relative speed: we can desire the solution without forming the relation between two quantities either speed or time.
Time = (L1+L2)/(relative speed);
L1-Length of train-1.
L2-Length of train-2.
Riyaz said:
1 decade ago
Hi friends. I have one doubt when the trains are moving in opposite direction we add the speed of those trains but why we have to add the length of the two trains. Please explain me.
Ramya said:
1 decade ago
How 5/18 came? Can you please explain me?
Santhu said:
10 years ago
Km/hr convert meter/sec=5/18 multiple.
Jyothi said:
10 years ago
km/hr = 1000 m/3600 sec = 5/18 m/sec [1000/3600 = 5/18].
Geenee said:
10 years ago
Why km is converted into meter though there all information is in kilometer?
Krishan said:
10 years ago
Why it is explicitly mentioned "time taken for faster train to cross slower train"?
I think time taken will be same for both the trains.
I think time taken will be same for both the trains.
Adm said:
10 years ago
But here don't we need to consider length of longer train only because faster will cross beforehand.
Adm said:
10 years ago
You have to add the lengths when you consider crossing each other and add speeds. For more understanding consider two trains moving at different speed and plot a graph for each sec as how much they cross each other and you will discover why the formula is:
Time for crossing = (Sum of length of two train)/(Sum of speed of two trains).
Time for crossing = (Sum of length of two train)/(Sum of speed of two trains).
(1)
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