Question

A car approaching a crossing `C` at a speed of `20 m//s` sounds a horn of frequency `500 H_(Z)` when `80 m` from the crossing . Speed of sound in air is `330 m//s` . What frequency is heard by an observer (at rest) `60m` from the crossing on the straight road which crosses car road at right angles ?

Answer 1

The situation is as shows in figure.
`cos theta = (80)/(100) = (4) /(5)`
`:.` Apparent frequency, `f_(app) = ((nu)/(nu- nu_(S) costheta))f`
= `((330)/(330 - 20 xx (4)/(5)))(500)`
= `52505 H_(Z)`