Question

An observer, who was initially 400 m from the marching band noticed that the band is approaching her at a constant rate of 0.75 m/s. Calculate the apparent frequency of the sound reaching the observer from this musical instrument.

Answer 1

Here we have given that,

Lambada = 400 m

Velocity Vs = 0.75 m/s

Nwo the observed frequency f = v/lambada = 0.75/400 = 0.001875 hz

Now we have the formula for apparent frequency as

f' = (V + Vo)/(V -Vs) × f

Here V = speed of sound waves = 343 m/s

Vo = speed of observer = 0

Vs = speed of source = 0.75 m/s

f = 0.001875 hz

f' = apparent frequency

Now on plugging the values we will get ,

f' = (343+0)/(343-0.75) × 0.001875 = 0.0018791088 hz which is our apparent frequency