Q. The driver of a car travelling with speed $30\ metres\ per\ second$ towards a hill sounds a horn of frequency $600\ Hz.$ If the velocity of sound in air is $330\ metres\ per\ second,$ the frequency of the reflected sound as heard by the driver is

A) $720\ Hz$
B) $555.5\ Hz$
C) $550\ Hz$
D) $500\ Hz$
Explanation

(a) Frequency of reflected sound heard by the driver.
$n^{'} = n\left\lbrack \frac{v - \left( - v_{o} \right)}{v - v_{s}} \right\rbrack = n\left\lbrack \frac{v + v_{o}}{v - v_{s}} \right\rbrack = n\left\lbrack \frac{v + v_{car}}{v - v_{car}} \right\rbrack$
$= 600\left\lbrack \frac{330 + 30}{330 - 30} \right\rbrack = 720\ Hz$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.

Want more practice?
Practice Waves MCQs