Q. A bus is moving with a velocity of $5\ ms^{- 1}$ towards a huge wall. The driver sounds a horn of frequency 165 Hz. If the speed of sound in air is $335ms^{- 1}$, the number of beats heard per second by the passengers in the bus will be
A) 3
B) 4
C) 5
D) 6
Explanation
(c) $v = 165\ Hz$, and
$v^{'} = \frac{335 + 5}{335} \times \frac{335}{330} \times 165 = 170Hz$
$\therefore$ Number of beats $s^{- 1}$
$= v^{'} - v = 170 - 165 = 5$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.