Question

A source of sound S is moving with a velocity of 50 m/s towards a stationary observer. The observer measures the frequency of the source as 1000 Hz. 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 $350m/s$)

• A. $857Hz$
• B. $807Hz$
• C. $750Hz$
• D. $1143Hz$

Answer 1

Answer: (C)

$750Hz$

$f_{app}=\left(\frac{v-0}{V-50}\right)f_{source}$

$1000=\left(\frac{350}{300}\right)f_{source}$

$f_{source}=\frac{1000\times 300}{350}$

$f_{app}=\left(\frac{V}{V+50}\right).f_{source}$

$=\frac{350}{400}\times 1000\times \frac{300}{350}$
$=750Hz$