A stationary police car emits a sound of frequency 1240 HzHz that bounces off of a car on the highway and returns with a frequency of 1275 HzHz. The police car is right next to the highway, so the moving car is traveling directly toward or away from it.

Answer

given,

frequency from Police car= 1240 Hz

frequency of sound after return  = 1275 Hz

Calculating the speed of the car = ?

Using Doppler's effect formula

Frequency received by the other car

  ..........(1)

u is the speed of sound = 340 m/s

v is the speed of the car

Frequency of the police car received

now, inserting the value of equation (1)

  1.02822(340 - v) = 340 + v

   2.02822 v = 340 x 0.028822

   2.02822 v = 9.799

   v = 4.83 m/s

hence, the speed of the car is equal to v = 4.83 m/s