Question

An engine driver moving towards a wall with a velocity of 50 ms${}^{-1}$ emits a note of frequency 1.2 kHz. The frequency of note after reflection from the wall as heard by the engine driver when the speed of sound in air is 350 ms${}^{-1}$ is

• A. 1 kHz
• B. 1.8 kHz
• C. 1.6 kHz
• D. 1.2 kHz

Answer 1

The correct option is C 1.6 kHz

$v=350m{s}^{-1}$

$v_0=50m{s}^{-1}$

$f=1.2kHz$

$f^{\prime }=f\left(\frac{v+v_0}{v-v_0}\right)$

$⟹1.2\left(\frac{350+50}{350-50}\right)$

$⟹1.6kHz$