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JEE Main 2021 (26 Aug, Shift 1) · Doppler Effect

Doppler Effect question from JEE Main 2021 (26 Aug, Shift 1)

Q44JEE Main 2021 · 26 AUG · SHIFT 1Easy

Doppler Effect

A source and a detector move away from each other in absence of wind with a speed of 20 m/s with respect to the ground. If the detector detects a frequency of 1800 Hz of the sound coming from the source, then the original frequency of source considering speed of sound in air 340 m/s will be ............... Hz.

Numerical answer type. Work it out, then open the answer.

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Answer: 2025

Moving apart: $n' = n\frac{v - v_o}{v + v_s}$ .
$1800 = n \times \frac{340 - 20}{340 + 20} = n \times \frac{8}{9}$
$n = 1800 \times \frac{9}{8} = 2025$ Hz

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