Question

From a vantage point very close to the track at a stock car race, you hear the sound emitted by a moving car. You detect a frequency that is 0.844 times smaller than that emitted by the car when it is stationary. The speed of sound is 343 m/s. What is the speed of the car?

Answer 1

Step-by-step explanation:

Given

Apparent Frequency
`f'=0.844 f_0`

speed of sound
`v=343 m/s`

Applying Doppler Effect Formula

`f'=f_0((v+v_0)/(v-v_s))`

where
`v_0=`speed of observer

`v_s=`speed of source

here
`v_o=0` as he is listening and at rest

`0.844f_0=f_0((343+0)/(343-v_s))`

`343-v_s=406.39`

`v_s=-63.39 m/s`

i.e. car is moving away from observer with 63.99 m/s