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