Answer:
Explanation:
We shall apply Doppler's effect to solve the problem .
Formula for apparent frequency for a source of sound approaching an observer is as follows .
f₁ = f₀ V / (V - v )
where f₁ and f₀ are apparent and real frequency of source , V and v is velocity of sound and velocity of approaching source respectively .
Putting the given values and knowing that speed of sound is 340 m /s
f₁ =346x 340 / (340 - 39.6 )
f₁ = 391.6 Hz
In case of receding train , the formula is
f₂ = f₀ V / (V + v )
Putting the values
f₂ = 346x 340 / (340 + 39.6 )
= 309.9 Hz
Change in frequency = 391.6 - 309.9
= 81.7 Hz .
