Question

A car is moving with a speed of 15 m/s towards a stationary wall. A person in the car pressed the horn and experienced a change in frequency of 40 Hz due to reflection from the stationary wall. Find the frequency of the horn. (Use 𝑣sound = 330 m/s)

Answer 1

$f= f_{0}(\frac{V+V_{c}}{V-V_{c}})$
$f= f_{0}(\frac{330+15}{330-15})$
$f= f_{0}\frac{345}{315}$
$f- f_{0}=40$
$f_{0}(\frac{345-315}{315})=40$
$f_{0}=\frac{40\times315}{30}$
$f_{0}=420Hz$

So, the answer is $420\ Hz$