15. Two trains of equal length running in opposite directions, pass a student standing
by a side of railway line in 18 secs. and 12 secs, respectively
. In what time will the two
trains cross each other?
Answers
Answer:
Time required to cross each other = 14.4 sec
Step-by-step explanation:
the lengths of the train be X
To cross a person a train has to travel the distance equal to it's own length
So
speed of two trains are = distance/ time taken
X / 18 ......for train say A
X / 12 .........for train say B
To cross them each other they will have to travel a distance equal to sum of their lengths = 2X
and the speed will be equal to the sum of their speeds as they are traveling in opposite direction.
speed = X /18 + X/12
Time required to cross each other
= 2X / ( X /18 + X/ 12)
= 2X / ( 2X/ 36 + 3X / 36)
= 2X ÷ ( 5X/36)
2X × 36
= --------------
5X
2 × 36
= ----------------
5
= 72 ÷ 5
= 14.4 sec