A siren of frequency 240 Hz is mounted on a vehicle moving at 60 m/s along a straight road. A stationary observer lies on the road ahead. The speed of sound is 300 m/s. What is the sudden drop in observed frequency as the vehicle passes the observer and changes from approaching to receding?
Options

Question

A siren of frequency 240 Hz is mounted on a vehicle moving at 60 m/s along a straight road. A stationary observer lies on the road ahead. The speed of sound is 300 m/s. What is the sudden drop in observed frequency as the vehicle passes the observer and changes from approaching to receding?

Options

G1 Physics · Accepted Answer

While approaching, f₁ = f×v/(v−uₛ) = 240×300/(300−60) = 240×300/240 = 300 Hz. After passing, while receding, f₂ = f×v/(v+uₛ) = 240×300/(300+60) = 240×300/360 = 200 Hz. Therefore, Δf = f₁−f₂ = 300−200 = 100 Hz. Correct option: C.