A sound source (S) emits frequency of 180 Hz when moving with velocity 5 m / s towards a moving wall moving with same speed as of source and a stationary observer (O) hears the sound. The situation is shown in the diagram. Find the number of beats per second heared by the observer. (Speed of sound =340 m / s )

Question

A sound source (S) emits frequency of 180 Hz when moving with velocity 5 m / s towards a moving wall moving with same speed as of source and a stationary observer (O) hears the sound. The situation is shown in the diagram. Find the number of beats per second heared by the observer. (Speed of sound =340 m / s ) (A)  (B)  (C)  (D)

Tardigrade Admin · Accepted Answer

Direct frequency received by O(f1)=((v-v1/v)) f frequency received by wall =f (No relative motion between S and wall) frequency received by O from wall (f2)=((v-v1/v)) f beat frequency =|f1-f2|=0

Direct frequency received by O(f1​)=(vv−v1​​)f frequency received by wall =f (No relative motion between S and wall) frequency received by O from wall (f2​)=(vv−v1​​)f beat frequency =∣f1​−f2​∣=0

Direct frequency received by $O (f_{1}) = (\frac{v - v _{1}}{v}) f$
frequency received by wall $= f$ (No relative motion between $S$ and wall)
frequency received by $O$ from wall $(f_{2}) = (\frac{v - v _{1}}{v}) f$ beat frequency $= ∣ f_{1} - f_{2} ∣ = 0$