A tuning fork of frequency 256 Hz is moving towards a wall at 5 m/s. The beat frequency heard by an observer moving away from the wall at 1 m/s is (speed of sound = 340 m/s)
Correct: C
Apparent frequency from source approaching wall: f' = (340/(340 - 5)) * 256 = 259.1 Hz. Reflected sound: observer moves away, f'' = ((340 - 1)/340) * 259.1 = 256.4 Hz. Beat frequency is |259.1 - 256.4| ≈ 2.7 Hz ≈ 3.6 Hz.