Q: A whistle giving out 450 Hz approaches a stationary observer at a speed of 33 m/s. the frequency heard by the observer (in Hz) is (speed of sound = 330 m/s)

(a) 409

(b) 429

(c) 517

(d) 500

Ans: (d)

Sol: As source is moving towards the observer

$\large f’ = \frac{v}{v-v_s} \times f$

$\large f’ = \frac{330}{330-33} \times 450 $

f’ = 500 Hz