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Q.
A bat moving at $10\, ms^{-1}$ towards a wall sends a sound signal of $8000\, Hz$ towards it. On reflection it hears a sound of frequency $f$. The value of $f$ in $Hz$ is close to (speed of sound = $320\, ms^{-1}$)
Observer $O$ at the wall receives a frequency, $f_{1}=f \frac{v}{v-v_{p}}$
Here $v=$ speed of sound $=320\, m / s$
On reflection from the wall, source $S$ received
$f_{2}=f_{1} \frac{v+v_{s}}{v}$
$\Rightarrow f_{2}=f \frac{v +v_{s}}{v-v_{s}}=8000\left(\frac{320+10}{320-10}\right)=8000 \times \frac{339}{3199}$
$\Rightarrow f_{2}=8516.12 \approx 8516\, Hz$
