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JEE Mains · Physics · STD 11 - Waves and sound
  • JEE Mains 2019
  • Medium
  • MCQ

Two sources of sound \(S_1\) and \(S_2\) produce sound waves of same frequency \(660\, Hz\). A listener is moving from source \(S_1\) towards \(S_2\) with a constant speed \(u\, m/s\) and he hears \(10\, beats/s\). The velocity of sound is \(330\, m/s\). Then, \(u\) equals ... \(m/s\)

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Answer & Solution

Correct Answer

(D) \(2.5\)

Step-by-step Solution

Detailed explanation

\(f=660\,Hz,\)     \(v=330\,m/s\)

\(f_{1}=f\left(\frac{v-u}{v}\right) ; \quad f_{2}=f\left(\frac{v+u}{v}\right)\)

\(\mathrm{f}_{2}-\mathrm{f}_{1}=\frac{\mathrm{f}}{\mathrm{v}}[\mathrm{v}+\mathrm{u}-(\mathrm{v}-\mathrm{u})]\)

\(10=\mathrm{f}_{2}-\mathrm{f}_{1}=\frac{\mathrm{f}}{\mathrm{v}}[2 \mathrm{u}]\)

\(u=2.5 \mathrm{m} / \mathrm{s}\)

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