Question

A sound source is falling under gravity. At sometime t = 0, the detector lies vertically below the source at a depth H as shown. If v is the velocity of sound and $f_o$ is frequency of the source, then the apparent frequency recorded after t = 2s is

• A. $f_0$
• B. $\frac{f_0(v+2g)}{v}$
• C. $\frac{f_0(v-2g)}{v}$
• D. $f_0(\frac{v}{v-2g})$

Answer 1

Answer: (D)

$f_0(\frac{v}{v-2g})$

Velocity of a source at a time t, falling under gravity is $v_s=gt$.

Now the apparent frequency recorded by the recorder at $t=2s$ is, $\overline{n}=f_0\frac{V}{V-V_s}=f_0\frac{V}{V-gt}=f_0\frac{V}{V-2g}$.