A bus is moving with a velocity of $5 \mathrm{~m} / \mathrm{s}$ towards a wall. The driver blows the horn of…
A bus is moving with a velocity of $5 \mathrm{~m} / \mathrm{s}$ towards a wall. The driver blows the horn
of frequency $165 \mathrm{~Hz}$. If the speed of sound in air is $335 \mathrm{~m} / \mathrm{s}$, then after reflection of
sound wave, the number of beats per second heard by the passengers in the bus will be
4
5
6
2
Solution
The number of beats heard by the passengers is determined by the Doppler effect. When the bus moves towards the wall, the frequency of the sound increases. After the sound reflects from the wall, the frequency heard by the passengers increases further. The number of beats per second is the difference between the original and the reflected frequencies.
The correct answer is:
(2) 5 beats per second.