# A source  of sound S is moving with a velocity of 50 m/s toward s a stationary observer ,The observer measurs the frequency of the source as 1000Hz .What will be the apparent frequency of the source when it is moving away from the observer after crossing him ? (take velocity of sound in air is 350m/s)Option 1)750 HzOption 2)857HzOption 3)1143HzOption 4)807Hz

$F_{1}=\left ( \frac{v}{v-Vs} \right )f$

$F_{2}=\left ( \frac{v}{v+Vs} \right )f$

$\frac{F_{1}}{F_{2}}=\left ( \frac{V+Vs}{V-Vs} \right )$

$\frac{1000}{F_{2}}=\frac{400}{300}$

$F_{2}=750Hz$

Option 1)

750 Hz

Option 2)

857Hz

Option 3)

1143Hz

Option 4)

807Hz

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