Question

A police car moving at $22\, m / s$, chases a motorcyclist. The police man sounds his horn at $176\, Hz$, while both of them move towards a stationary siren of frequency $165\, Hz$. Calculate the speed of the motorcycle, if it is given that he does not observes any beats

• A. 33 m/s
• B. 22 m/s
• C. Zero
• D. 11 m/s

Answer 1

Answer: (B)

$n_{1}=$ Frequency of the police car horn observer heard by motorcyclist
$n_{2}=$ Frequency of the siren heard by motorcyclist.
$v_{2}=$ Speed of motor cyclist
$n_{1}=\frac{330-v}{330-22} \times 176;$
$n_{2}=\frac{330+v}{330} \times 165$
$\because n_{1}-n_{2}=0$
$\Rightarrow v=22\, m / s$