Question

The speed of sounds in air at a given temperature is 350 m/s. An engine blows whistle at a frequency of 1200 c/s. It is approaching the observer with velocity 50 m/s. The apparent frequency in c/s heard by the observer will be :

• A. 600
• B. 1050
• C. 1400
• D. 2400

Answer 1

The correct option is C 1400

$v=350m/s$

$v_s=velocityofsource=50m/s$

$n_0=1200Hz$

$\because$ the source is approaching towards observer the apparent frequency is

$\therefore$ $n^1=\left(\frac{v}{v-vs}\right)n_0$

$\therefore$ $n^1=\left(\frac{350}{350-50}\right)1200$

$\therefore$ $n^1=\left(\frac{350}{300}\right)1200$

$\therefore$ $n^1=350\times 4$

$\therefore$ $n^1=1400Hz....ans$