A radar sends out a sound wave of 1.50 Mhz and senses it again from a moving car at a 1.40 Mhz.
What is the speed of the car ?
If the detector (radar)is at rest and the source (moving car that reflects the sound)) is moving away from the detector, the observed frequency f is less than the actual frequency f₀.
The speed of sound v =343 m/s
f=f₀v/(v+V)
V=v(f₀-f)/f =343•(1.5-1.4)•10⁶/1.4•10⁶=24.5 m/s