Physics - Sound Wave Question with Solution | TestHub

An observer is riding on a bicycle and moving towards a hill at$18 \mathrm{km} {\mathrm{h}}^{-1}$. He hears a sound from a source at some distance behind him directly as well as after its reflection from the hill. If the original frequency of the sound as emitted by source is$640 \mathrm{Hz}$and velocity of the sound in air is$320 \mathrm{m} {\mathrm{s}}^{-1}$, the beat frequency between the two sounds heard by observer will be _____$\mathrm{Hz}$.