A toy-car,blowing its horn,is moving with a s | vedclass

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(D) Let $f$ be the frequency of the horn.The observer hears two sounds: one directly from the car and one reflected from the wall.$1$. Frequency of so

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$167$

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(D) Let $f$ be the frequency of the horn.The observer hears two sounds: one directly from the car and one reflected from the wall.$1$. Frequency of sound heard directly from the car $(f_1)$: Since the car is moving away from the observer (assuming the observer is behind the car or the car is moving away from the observer's position),but the problem states the car is moving towards the observer,we use the Doppler formula: $f_1 = f \left( \frac{v}{v - v_s} ight) = f \left( \frac{340}{340 - 5} ight)$.$2$. Frequency of sound reflected from the wall $(f_2)$: The wall acts as a source. The sound hits the wall at $f' = f \left( \frac{340}{340 + 5} ight)$ and reflects back to the observer. Since the observer is stationary,$f_2 = f' = f \left( \frac{340}{340 + 5} ight)$.Beat frequency is given by $|f_1 - f_2| = 5$.$5 = f \left( \frac{340}{335} - \frac{340}{345} ight) = 340f \left( \frac{345 - 335}{335 	imes 345} ight) = 340f \left( \frac{10}{115575} ight)$.$f = \frac{5 	imes 115575}{3400} \approx 170\, Hz$.

$A$ toy-car,blowing its horn,is moving with a steady speed of $5\, m/s$,away from a wall. An observer,towards whom the toy car is moving,is able to hear $5\, beats$ per second. If the velocity of sound in air is $340\, m/s$,the frequency of the horn of the toy car is close to ... $Hz$

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