Question

The apparent frequency of the whistle of an engine changes in the ratio of 6:5 as the engine passes a stationary observer. If the velocity of sound is 330 m/s, then the velocity of the engine is

• A. 3 m/s
• B. 30 m/s
• C. 0.33 m/s
• D. 660 m/s

Answer 1

The correct option is B 30 m/s

$v^{\prime }=\frac{v}{v-v_s}v,v"=\frac{v}{v+v_s}v\frac{v^{\prime }}{v^{\prime \prime }}=\frac{v+v_z}{v-v_s}or\frac{6}{5}=\frac{330+v}{330-v}11v_s=330\Rightarrow v_s=30m/s$