Two trains move towards each other with the same speed.

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Two trains move towards each other with the same speed. The speed of sound is 340 m/s. If the height of the tone of the whistle of one of them heard on the other changes 9/8 times, then the speed of each train should be

Here, v' =	9	v
	8

Source and observer are moving in opposite direction, therefore, apparent frequency

v' = v &time;	(v + u)
	(v - u)

9	v = v &time;	340 + u
8		340 - u

⇒ 9 &time; 340 - 9u = 8 &time; 340 + 8u

⇒ 17u = 340&time; 1 ⇒ u =	340	= 20 m/sec.
	17