Question

c) 27m/s
The apparent frequency of the whistle of an engine changes in the ratio 6:5 as engine
passes a stationary observer. If the speed of sound is 352 m/s. Then the speed of engine
will be
f
A) 22 m/s
C)
27 m/s
B) 3
2 m/s
D) 36 m/s
​

Answer 1

Answer:

85 m/s

Explanation:

ANSWER

Given : Velocity of sound     vsound=340m/s

Let the frequency of the whistle be n and velocity of the engine be v.

Let the apparent frequencies heard by the observer be  n′  and n′′ before and after the source passes the observer.   

Doppler effect when source   (S′)   approaches the stationary observer:

n′=n[vsound−vsourcevsound] =n[340−v340]

Doppler effect when source  S   moves away from the stationary observer:

n′′=n[vsound+vsourcevsound] =n[340+v340]

Now      n′′n′=35       (Given)

⟹340−v340+v=35

Thus   v=85m/s