Physics Question on Electromagnetic waves

Question

A stationary police car sounds a siren with a frequency of 990 Hz. If the speed of sound is 330 m/s, an observer, driving towards the car with a speed of 33 m/s, will hear a frequency of

Answer 1

Solution

From Doppler's effect the perceived frequencyf' is given by $\hspace25mm f' = f \bigg(\frac{v + v_0}{v}\bigg)$ Given, $f = 990 Hz, v = 300\, m/s$ and $v_0 = 33\, m/s$ $\therefore \hspace15mm f' = 900 \bigg(\frac{330+ 33}{330}\bigg)$ $\hspace25mm = 900 \times \frac{363}{300} = 1089\, Hz$