Question

With what velocity an observer should move relative to a stationary source so that he hears a sound of double the frequency of source

• A. Velocity of sound towards the source
• B. Velocity of sound away from the source
• C. Half the velocity of sound towards the source
• D. Double the velocity of sound towards the source

Answer 1

Answer: (A)

Velocity of sound towards the source

By using $n^{\prime }=n\left(\frac{v}{v-v_s}\right)$

$2n=n\left(\frac{v-v_0}{v-0}\right)$

$\Rightarrow v_0=-v=-$(Speed of sound)

Negative sign indicates that observer is moving opposite to the direction of velocity of sound, as shown