JEE Mains · Physics · STD 11 - Waves and sound
- JEE Mains 2023
- Hard
- Numerical
A person driving car at a constant speed of \(15\,m / s\) is approaching a vertical wall. The person notices a change of \(40\,Hz\) in the frequency of his car's horn upon reflection from the wall. The frequency of horn is ............ \(Hz\). (Given : Speed of sound : \(330\,m / s\) )
Pick an option to check your answer.
Answer & Solution
Correct Answer
(D) \(420\)
Step-by-step Solution
Detailed explanation
\(\text { Frequency of reflected sound }=\left(\frac{ v + v _{ c }}{ v - v _{ c }}\right) f _0\)
\(f =\left(\frac{330+15}{330-15}\right) \times f _0\)
\(=\frac{345}{315} f _0\)
\(\frac{345}{315} f _0- f _0=40\)
\(\frac{30}{315} f _0=40\)
\(f _0=\frac{4 \times 315}{3}=420\,Hz\)
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