A train S 1 , moving with a uniform velocity of 108 k m / h , approaches another train S 2 standing on a platform. An observer O moves with a uniform velocity of 36 k m / h towards S 2 , as shown in figure. Both the trains are blowing whist

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A train S 1 , moving with a uniform velocity of 108 k m / h , approaches another train S 2 standing on a platform. An observer O moves with a uniform velocity of 36 k m / h towards S 2 , as shown in figure. Both the trains are blowing whistles of same frequency 120 H z . When O is 600 m away from S 2 and distance between S 1 and S 2 is 800 m , the number of beats heard by O is____ [Speed of the sound = 330 m / s ]

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Speed of sound= 300 m s Calculate beat f r e q f b = f 1 - f 2 Where, f 1 and f 2 are the apparent frequencies of train S 1 and S 2 observed by observer. ∴ Using Doppler's effect, ⇒ f b = 120 330 + 10 c o s 53 ° 330 - 30 c o s 37 ° - 330 + 10 330 = 120 336 306 - 34 33 = 8.128 H z

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