Question

A source of sound of frequency 90 vibration/sec is approaching a stationary observer with a speed equal to 1/10 the speed of sound. What will be the frequency heard by the observer

• A. 80 vibration/sec
• B. 90 vibration/sec
• C. 100 vibration/sec
• D. 120 vibration/sec

Answer 1

Answer: (C)

100 vibration/sec

Answer 2

$n' = \frac{v}{v - v_{s}}.n$ ⇒ $n' = \frac{v}{v - \frac{v}{10}}.n$ ⇒ $n' = \frac{10}{9}n = \frac{10 \times 90}{9} = 100$

vibration/sec