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

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia