Question

An observer starts moving with uniform acceleration a towards a stationary sound source of frequency $f_o$. As the observer approaches the source, the apparent frequency f heard by the observer varies with time t as

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

$f=f_0\frac{(v+v_0)}{v}$

$=f_0\left(\frac{v+at}{v}\right)=f_0+\frac{f_{0}a}{v}t$

This is an equation of a straight line with positive intercept fo and positive slope $\frac{f_{o}a}{v}$ , where v is the speed of sound in air.