Two men are walking along a horizontal straight line in the same direction. The man in front walks at a speed 1.0 m s - 1 and the man behind walks at a speed 2.0 m s - 1 . A third man is standing at a height 12 m above the same horizontal l

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Two men are walking along a horizontal straight line in the same direction. The man in front walks at a speed 1.0 m s - 1 and the man behind walks at a speed 2.0 m s - 1 . A third man is standing at a height 12 m above the same horizontal line such that all three men are in a vertical plane. The two walking men are blowing identical whistles which emit a sound of frequency 1430 H z . The speed of sound in air is 330

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Correct answer: 0

cos ⁡ θ = 5 13 f A = 1430 330 330 - 2 cos ⁡ θ = 1430 1 1 - 2 cos ⁡ θ 330 = 1430 1 + 2 cos ⁡ θ 330 (By binomial expansion) f B = 1430 330 330 + 1 cos ⁡ θ = 1430 1 - cos ⁡ θ 330 ∆ f = f A - f B = 1430 3 cos ⁡ θ 330 = 13 cos ⁡ θ = 13 5 13 = 5.00 H z

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