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.

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

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

answer: option c. i.e. electric current flowing “downhill” from the negative electrode to the positive electrode in a battery

explanation:

the water analogy to the circuits define the pipes (water flows) to the electric current. now, we know that the electric current flows from the positive terminal to the circuit (as shown in the diagram attached).

hence, option c is the correct answer.