Question

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?

Answer 1

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

then

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

So,

20010 = (343 - Vo)*20000/(343 - 40)

Vo = 343 - 20010*303/20000

Vo = 39.85 m/sec = Speed of your car.

Please Upvote.