Question

Two cars $A$ and $B$ are moving away from each other in opposite directions. Both the cars are moving with a speed of $20m/s$ with respect to the ground. If an observer in car $A$ detects a frequency $2000Hz$ of the sound coming from car $B$, what is the natural frequency of the sound source in car $B$ ? (speed of sound in air $=340m/s$ )

• A. $2300Hz$
• B. $2150Hz$
• C. $2060Hz$
• D. $2250Hz$

Answer 1

The correct option is D $2250Hz$

Formula used: $f=\frac{v+v_0}{v-v_s}{f}_0$
As we know

$f=\frac{v+v_0}{v-v_s}{f}_0$

($v_0$ and $v_s$ is taken approaching to each other)

$2000=\frac{340+(-20)}{340-(-20)}{f}_0$

$f_0=2250Hz$