An observer moves towards a stationary source of sound, with a velocity one-fifth of the velocity of sound. What is the percentage increase in the apparent frequency?

When observer moves towards stationary source then apparent frequencyn' = [v+v0v]n = [v+v5v]n = 65n = 1.2 nIncrement in frequency = 0.2 n so percentage change infrequency = 0.2nn×100 = 20%