A person is observing two trains one coming towards him and other leaving with the same velocity 4 m / s . If their whistling frequencies are 240 Hz each, then the number of beats per second heard by

Question

A person is observing two trains one coming towards him and other leaving with the same velocity 4 m / s . If their whistling frequencies are 240 Hz each, then the number of beats per second heard by the person will be : (if velocity of sound is 320 m / s )

TestHub · Accepted Answer

Observed frequency of first train n 1 ​ ​ = v − v s ​ v ​ × n = 320 − 4 320 ​ × 240 = 316 320 ​ × 240 = 243 Hz . ​ Observed frequency of second train n 2 ​ ​ = v + v s ​ v ​ n = 320 + 4 320 ​ × 240 = 237 Hz . ​ ∴ Number of beats = 243 − 237 = 6

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