Q 11-14-114JEE MainJEE Main 2019 (10 Apr, Shift 1)Easy
A stationary source emits sound waves of frequency $500\ \text{Hz}$. Two observers moving along a line passing through the source detect sound to be of frequencies $480\ \text{Hz}$ and $530\ \text{Hz}$. Their respective speeds are, in $\text{m s}^{-1}$, (Given speed of sound $= 300\ \text{m/s}$)
Answer: (C) $12,\ 18$
The first observer hears a lower frequency, so is moving away: $480 = 500\,\dfrac{300 - v_1}{300}$, giving $v_1 = 12\ \text{m/s}$.
The second hears a higher frequency, so is approaching: $530 = 500\,\dfrac{300 + v_2}{300}$, giving $v_2 = 18\ \text{m/s}$.
Solution by Sreeraj P, M.Sc Physics