NEET Physics MCQs

A siren emitting a sound of frequency 800 Hz moves away from an observer towards a cliff at a speed of ${\rm{15}}\,{\rm{m}}{{\rm{s}}^{{\rm{ - 1}}}}{\rm{.}}$ Then, the frequency of sound that the observer hears in the echo reflected from the cliff is:

(Take velocity of sound in air ${\rm{ = }}\,{\rm{330}}\,{\rm{m}}{{\rm{s}}^{{\rm{ - 1}}}}$)