A source of sound is travelling towards a stationary observer. The frequency of sound heard by the observer is of three times the original frequency. The velocity of sound is $v\, m/sec.$ The speed of source will be
A$\frac{2}{3}v$
B$v$
C$\frac{3}{2}v$
D$3v$
Medium
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A$\frac{2}{3}v$
a $n' = n\,\left( {\frac{v}{{v - {v_S}}}} \right)$
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