A whistle producing sound waves of frequencies $9500\ Hz$ and above is approaching a stationary person with speed $v\ ms^{-1}$. The velocity of sound in air is $300\ ms^{-1}$. If the person can hear frequencies upto a maximum of $10,000\ Hz$, the maximum value of $v$ upto which he can hear whistle is ... $ms^{-1}$
AIEEE 2006, Medium
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$v^{\prime}=v\left[\frac{v}{v-v_{s}}\right] \Rightarrow 10000=9500\left[\frac{300}{300-v}\right]$
$\Rightarrow 300-\mathrm{v}=300 \times 0.95 \Rightarrow \mathrm{v}=300-285=15 \mathrm{ms}^{-1}$
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