Two cars are approaching each other at an equal speed of 7.2 , km… - Vidyadip

MCQ

Two cars are approaching each other at an equal speed of $7.2\, km / hr$. When they see each other, both blow horns having frequency of $676\, Hz$. The beat frequency heard by each driver will be $.....\, Hz$. [Velocity of sound in air is $340\,m / s .]$

✓
$8$
B
$16$
C
$32$
D
$24$

✓

Answer

Correct option: A.

$8$

a
Frequency of sound heard by car$-1,$ which comes by reflection from car$-2$

$f _{1}= f _{0}\left(\frac{340+2}{340-2}\right)\left(\frac{340+2}{340-2}\right)$

$= f _{0}\left(\frac{342}{338}\right)^{2}$

Frequency of sound coming directly from car$-2$

$f _{2}= f _{0}\left(\frac{340+2}{340-2}\right)$

$\therefore f _{1}- f _{2}= f _{0}\left(\frac{342}{338}\right)\left(\frac{342}{338}-1\right)=8.09 \simeq 8$

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