Question

What is the frequency of the siren when cyclist is stationary?

Answer 1

We can use the doppler effect general case:

`f^(\prime)=(v\pm v_o)/(v\pm vs)f`

Where:

f' = Observed frequency = 894hz

v = velocity of sound waves = 343m/s

vo = Velocity of the observer = 24.5m/s

vs = Velocity of the source = 0

Since the observer alone is in motion towards the source:

`\begin{gathered} f^(\prime)=f\cdot(v+v_o)/(v) \\ 894=f\cdot(343+24.5)/(343) \\ 894=f\cdot(367.5)/(343) \\ f=(894)\cdot(343)/(367.5) \\ f=834.4Hz \end{gathered}`

Answer:

834.4 Hz