Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 14)
14.
Two trains 140 m and 160 m long run at the speed of 60 km/hr and 40 km/hr respectively in opposite directions on parallel tracks. The time (in seconds) which they take to cross each other, is:
Answer: Option
Explanation:
| Relative speed = (60 + 40) km/hr = |  |
100 x | 5 |  m/sec |
= | |
250 | m/sec. |
| 18 | 9 |
Distance covered in crossing each other = (140 + 160) m = 300 m.
| Required time = | |
300 x | 9 | sec |
= | 54 | sec = 10.8 sec. |
| 250 | 5 |
Discussion:
42 comments Page 5 of 5.
Lokesh said:
10 years ago
How can come 54/5 = 10.8?
Praveen said:
10 years ago
Let time is x sec. According to question:
Speed = Length/Time.
Both are in opposite so we add the speed if in same direction then sub speed.
So speed = 60+40 = 100 km/h.
We convert it in m/s by multiply 5/18.
So speed = 250/9 m/s.
Length = 140 m + 160 m = 300 m.
And time = x sec.
So 250/9 = 300/x.
So x = (300*9)/250.
And time = 10.8 sec.
Speed = Length/Time.
Both are in opposite so we add the speed if in same direction then sub speed.
So speed = 60+40 = 100 km/h.
We convert it in m/s by multiply 5/18.
So speed = 250/9 m/s.
Length = 140 m + 160 m = 300 m.
And time = x sec.
So 250/9 = 300/x.
So x = (300*9)/250.
And time = 10.8 sec.
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