Two identical organ pipes, each 0.80 m long and open at both ends, are mounted coaxially on a platform. One pipe remains at rest while the other is moved straight towards a stationary listener at 4 m s⁻¹. Both pipes are excited simultaneously in their fundamental modes. (Speed of sound in air = 340 m s⁻¹.)
(i) Calculate the beat frequency heard by the listener.
(ii) To eliminate the beats while the pipe continues to move at 4 m s⁻¹, to what length must the moving pipe be adjusted (still sounding in its fundamental mode)?