A police car is chasing a car at 40m/s. If the siren transmit at a frequency of 20000 Hz and you hear 20010 from your car. What is your velocity?
Using doppler's effect
Here Source of sire = Police car
Observer = you in your car
So scenario according to doppler is
When the Source is approaching the Stationary observer and observer moving away from it
f1 = (V - Vo)*f0/(V - Vs)
V = Velocity of sound = 343 m/sec
Vs = Speed of police car = 40 m/sec
Vo = Speed of your car = ?
f0 = Source frequency = 20000 Hz
f1 = frequency heard by you = 20010 Hz
20010 = (343 - Vo)*20000/(343 - 40)
Vo = 343 - 20010*303/20000
Vo = 39.85 m/sec = Speed of your car.
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