Question

1. A car drives by at 20mph, with a violinist in it playing a song. The speed of sound is 343 m/s. The violin is actually playing at 800Hz, what frequency do you hear before and after the car passes you?

Answer 1

Answer:

frequency when car is approaching comes out to be 821 Hz

car is moving away from the object comes out to be 780 Hz

Explanation:

car speed = 20 mph = 8.94 m/s

speed of sound = 343 m/s

violin frequency = 800 Hz

when car is approaching:

$f^{'}= f(\dfrac{c+v_0}{c-v_s}) =800(\dfrac{343+0}{343-8.94}) =821 Hz$

when car is moving away

$f^{'}= f(\dfrac{c+v_0}{c+v_s}) =800(\dfrac{343+0}{343+8.94}) =780Hz$

hence the frequency when car is approaching comes out to be 821 Hz

and when the car is moving away from the object comes out to be 780 Hz