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Two trains, each moving with a velocity of 30m/s, cross each other. One of the trains gives a whistle whose frequency is 600Hz. If the speed of sound is 330m/s, the apparent frequency for passengers sitting in the other train before crossing would be __________

(a) 600Hz

(b) 630Hz

(c) 930Hz

(d) 720Hz

I had been asked this question in an international level competition.

This intriguing question comes from Stationary Waves in portion Waves of Engineering Physics I

1 Answer

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Best answer
Right answer is (d) 720Hz

Best explanation: γ^‘=v/(v-vs)×γ

=(330+30)/(330-30)×600

360/300×600=720Hz.

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