A car is moving towards a huge wall with a speed = c/10, where c = speed of sound in still air. A wind is also blowing parallel to the velocity of the car in the same direction and with the same speed. If the car sounds a horn of frequency f, then what is the frequency of the reflected sound of the horn heard by driver of the car?
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Question

A car is moving towards a huge wall with a speed = c/10, where c = speed of sound in still air. A wind is also blowing parallel to the velocity of the car in the same direction and with the same speed. If the car sounds a horn of frequency f, then what is the frequency of the reflected sound of the horn heard by driver of the car?

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G1 Physics · Accepted Answer

Step 1: Use superposition at the boundary. Reflection from a denser/fixed boundary introduces phase reversal; from a free boundary it does not. Step 2: Energy ratio gives amplitude ratio through I ∝ A² for waves in the same medium. Step 3: Combine incident, reflected and transmitted waves with the proper direction. Final: D: 11f/9.