Question

Two cars honking at the same frequency of 800 Hz are moving toward a pedestrian standing at the curb. One car is moving with speed 25 m/s, and the second car is moving at 21 m/s. What is the frequency of the beats heard by the pedestrian? Take the speed of sound as 343 m/s.

Answer 1

The frequency of the beats heard by the pedestrian is 9.33 Hz

Step-by-step explanation:

Frequency of the two cars, F = 800 Hz

speed of sound in air, V = 343 m/s

The sound wave length, λ = ?

λ = V / F

λ = 343 / 800

λ = 0.42875 m

The frequency of the car moving at 25 m/s heard by the pedestrian

f₁ = v₁ / λ

f₁ = 25 / 0.42875

f₁ = 58.31 Hz

The frequency of the car moving at 21 m/s heard by the pedestrian

f₂ = v₂ / λ

f₂ = 21 / 0.42875

f₂ = 48.98 Hz

The beat frequency = f₁ - f₂

= 58.31 - 48.98

= 9.33 Hz

Therefore, the frequency of the beats heard by the pedestrian is 9.33 Hz