JEE Main & Advanced
JEE Main Paper (Held on 12-4-2019 Morning)
question_answer
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 n. The value of n is close to: [JEE Main Held on 12-4-2019 Morning] (Speed of sound in water \[=1500\text{ }m{{s}^{1}}\])
A)499 Hz
B)502 Hz
C)507 Hz
D)504 Hz
Correct Answer:
B
Solution :
\[{{f}_{0}}=500Hz\]frequency recieved by A\[\Rightarrow \left( \frac{1500-5}{1500-7.5} \right){{f}_{0}}={{f}_{1}}\]and frequency recieved By B again \[\xleftarrow[{}]{{}}1500\] \[\begin{align} & (B) \\ & 7.5m/s\xrightarrow[{}]{{}} \\ \end{align}\] \[\begin{align} & (A)\And \Rightarrow \\ & \xrightarrow[{}]{{}}5m/\sec \\ \end{align}\] \[{{f}_{2}}=\left( \frac{1500+7.5}{1500+5} \right)\times \left( \frac{1500-5}{1500-7.5} \right){{f}_{0}}=502Hz.\]