Answer:
Option A
Explanation:
$36 km/h^{-1}=36 \times \frac{5}{18} =10 ms ^{-1}$
Apparent frequency of sound heard by car driver (observer) reflected from the
building will be
$f'= f\left(\frac{v+v_{0}}{v-v_{s}}\right)$
$= 8\left(\frac{320+10}{320-10}\right)$
=8.5 kHz
$\therefore$ Correct option is (a)
Analysis of question
(i) Question is simple
(ii) Driver will listen to two sounds, direct and reflected. Direct sound will be of 8 kHz as the driver has no relative motion with the car. But the reflected sound is of increased frequency because driver and image of car both are approaching each other
