Answer:
The speed of approaching police car is 5.35 m/s.
Explanation:
Given :
Police car actual frequency = 570 Hz
No of beats heard by stationary observer = 9
The speed of sound = 340 m/s
Beats is nothing but the difference of the frequency that heard by the observer.
According to the doppler equation,
⇒
Where = observed frequency, = actual frequency, = speed of sound,
= speed of observer, = speed of source.
One car approach stationary listener ( = )
∴ = ×
One car parked, so ( ) and
∴ =
From beats,
∴ no. of beats.
Where = frequency of approaching car, = frequency of stationary car.
∴ × =
While solving above equation,
∴ 5.35 m/s.
Therefore, the speed of approaching police car is 5.35m/s.