Question

. A stationary source produces a note of frequency 350 Hz. An observer in a car moving towards the source measures the frequency of sound as 370 Hz. Find the speed of the car. What will be the frequency of sound as measured by the observer in the car if the car moves away from the source at the same speed. (Assume speed of sound = 340 m/s) (Ans : Speed of car = 19.43 m/s, Frequency of the sound as measured by the observer in the car = 329.41 Hz)

Answer 1

Given :

frquency=n = 350 Hz

v = 340 m/s n

observere in the car measures frequency as =a = 370 Hz

When the car moves towards the stationary source then na = n (v+vo)/v

When the car moves towards the stationary source then na = n (v-v0)v

na = n (v+vo)/v

370 = 350 (340+vo/ 340)

359.42=340+vo

Vo=19.43m/s

Na= n (v-v0)v

na = 350( 340 – 20 /340) = 35/ 34 × 320  

∴ na = 329.41 Hz

∴Speed of car = 19.43 m/s, Frequency of the sound as measured by the observer in the car = 329.41 Hz

Answer 2

Given :

frquency=n = 350 Hz

v = 340 m/s n

observere in the car measures frequency as =a = 370 Hz

When the car moves towards the stationary source then na = n (v+vo)/v

When the car moves towards the stationary source then na = n (v-v0)v

na = n (v+vo)/v

370 = 350 (340+vo/ 340)

359.42=340+vo

Vo=19.43m/s

Na= n (v-v0)v

na = 350( 340 – 20 /340) = 35/ 34 × 320  

∴ na = 329.41 Hz

∴Speed of car = 19.43 m/s, Frequency of the sound as measured by the observer in the car = 329.41 Hz