A police van moving with velocity 22 m s⁻¹ and emitting sound of frequency 176 Hz, follows a motor cycle in turn is moving towards a stationary car and away from the police van. The stationary car is emitting frequency 165 Hz. If motorcyclist does not hear any beats then his velocity is (vs = 330 m s⁻¹)
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Question

A police van moving with velocity 22 m s⁻¹ and emitting sound of frequency 176 Hz, follows a motor cycle in turn is moving towards a stationary car and away from the police van. The stationary car is emitting frequency 165 Hz. If motorcyclist does not hear any beats then his velocity is (vs = 330 m s⁻¹)

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G1 Physics · Accepted Answer

Step 1: Beat frequency is fᵦ = |f₁ − f₂|. Step 2: Use how loading, shortening, tension change or motion changes the unknown frequency. Step 3: Select the value consistent with the stated increase/decrease of beat frequency. Final: A: 22 m s⁻¹.