25.Two trains are approaching each other on parallel tracks with same velocity.The whistle sound by one train is heard by a passenger in another train.If actual frequency of whistle is 620HZ and apparent increase in its frequency is 100Hz, the velocity of one of the two trains is (velocity of sound in air=335m/s)---------

actual frequency f0 = 620Hzapparent frequency =f = 620+100 = 720Hzf =v+vlv+vsf0vi=velocity of the listner which is positive as listner move towards the sourcevs = velocity of the source which is negative as source is moving towads the listnersince both have same velocity s720  = 335+s335-s62072(335-s) = 62(335-s)24120-72s =20770s-62s3350 = 10 ss= 335 m/s

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