JEE PYQ: Waves And Sound Question 34
Question 34 - 2019 (12 Apr Shift 1)
A submarine (A) travelling at 18 km/hr is being chased along the line of its velocity by another submarine (B) travelling at 27 km/hr. B sends a sonar signal of 500 Hz to detect A and receives a reflected sound of frequency $v$. The value of $v$ is close to :
(Speed of sound in water = 1500 ms$^{-1}$)
(1) 504 Hz
(2) 507 Hz
(3) 499 Hz
(4) 502 Hz
Show Answer
Answer: (4)
Solution
$f_1 = f\left(\frac{v - v_0}{v - v_s}\right) = f\left(\frac{1500 - 5}{1500 - 7.5}\right)$
No reflected signal,
$f_2 = f_1\left(\frac{v + v_0}{v + v_s}\right) = f_1\left(\frac{1500 + 7.5}{1500 + 5}\right)$
$f_2 = 500 \cdot \frac{1500 - 5}{1500 - 7.5} \cdot \frac{1500 + 7.5}{1500 + 5}$
$= 502$ Hz
BETA
