Q 11-14-094JEE MainJEE Main 2021 (27 Aug, Shift 1)Easy
Two cars $X$ and $Y$ are approaching each other with velocities $36$ km h$^{-1}$ and $72$ km h$^{-1}$ respectively. The frequency of a whistle sound as emitted by a passenger in car $X$, heard by the passenger in car $Y$ is $1320$ Hz. If the velocity of sound in air is $340$ m s$^{-1}$, the actual frequency of the whistle sound produced is ______ Hz.
Numerical value type. Enter your answer.
Answer: 1210
Source $X$: $v_s = 10$ m s$^{-1}$; observer $Y$: $v_o = 20$ m s$^{-1}$, approaching each other.
$$f' = f\,\frac{v + v_o}{v - v_s} = f\,\frac{360}{330} \Rightarrow f = 1320\times\frac{330}{360} = 1210\ \text{Hz}$$
Solution by Sreeraj P, M.Sc Physics