Q.
An observer starts moving with uniform acceleration, towards a stationary sound source of frequency f0 . As the observer approaches the source, the apparent frequency (f) heard by the observer varies with time ( t ) is
Let v be the speed of sound in air, vL velocity of observer at time t. As the observer approaches the source, therefore, apparent frequency f=v(v+vL)f0=[vv+(0+at)]f0=f0+(vf0at)
This is the equation of a straight line with a positive intercept (f0) and positive slope (vf0a) .