Two sources of sound ${\mathrm{S}}_1\mathrm{and}{\mathrm{S}}_2$ are at some distance apart. A person is at some point between ${\mathrm{S}}_1\mathrm{and}{\mathrm{S}}_2$  on the line joining them. Each of the sources emits sound with frequency  ${\mathrm{f}}_0.$ The source  ${\mathrm{S}}_1$ starts moving away from the person with velocity $\frac{\mathrm{v}}{\mathrm{n}}$  and the source  ${\mathrm{S}}_2$ starts moving towards the listener with velocity$\frac{\mathrm{v}}{\mathrm{n}}$.  If velocity of sound in air is V, find the beat frequency heard by the person.

• A

  $\frac{{\mathrm{f}}_{\mathrm{o}}}{\left({\mathrm{n}}^2+1\right)}$

• B

  $\frac{{\mathrm{f}}_{\mathrm{o}}}{\left({\mathrm{n}}^2-1\right)}$

• C

  $\frac{2{\mathrm{nf}}_{\mathrm{o}}}{\left({\mathrm{n}}^2-1\right)}$

• D

  $\frac{4{\mathrm{nf}}_{\mathrm{o}}}{\left({\mathrm{n}}^2-1\right)}$