Question

A police car siren emits a

frequency of
2010 Hz when stationary. Another car
hears a 1920
1920 Hz sound when it drives
away from the stationary police car.
How fast is the second car driving?

Answer 1

Answer: 15.35 m/s

Explanation: 15.35 m/s

`$$From the Doppler effect$$f^(\prime)=\left((v \pm v_(0))/(v \pm v_(s))\right) f_(s)$$`

`\begin{aligned}&f^(\prime)=1920 \mathrm{~Hz} ; \ \ V=343 \mathrm{~m} / \mathrm{s} \\&f=2010 \mathrm \ \text{{H}z} \\&V_S=0 \text { As police car is stationary }\end{aligned}`

`\begin{aligned}1920 &=\left((343 \pm v_(0))/(343)\right) * 2010 \\1920 &=\left((343-v_(0))/(343)\right) * 2010 \\ -v_(0) &=-15.35 \mathrm{~m/s} \\v_(0) &=15.35 \mathrm{~m} / \mathrm{s}\end{aligned}`

Therefore, the second car is driving at 15.35 m/s