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1.	A source is moving towards the observer with the speed of 40 m/s and emitting the sound of frequency 100 Hz. Find the observed frequency by standing observer if the velocity of propagation of sound is 340 m/s.1. 89 Hz2. 113 Hz3. 110 Hz4. 230 Hz
Answer» Correct Answer - Option 2 : 113 Hz CONCEPT: Doppler Effect:Anincrease or decreasein the frequency of sound,light, or other waves that are observed by the observer due to movement ofthe source and observer towards (or away from) each other is known as Doppler Effect. Theapparent frequencyheard by the observer is given by the formula: \(f=f_0\left ( \frac{v\pm v_o}{v \pm v_s} \right )\) where f is apparent frequency, f0is the original frequency of the source, v is the speed of sound in air, vsis the speed of the source, vois the speed of the observer. CALCULATION: Given that v = 340 m/s; vs= 40m/s (-ve) moving towards; v0= 0; f = 100 Hz \(f=f_0\left ( \frac{v\pm v_o}{v \pm v_s} \right )\) \(f=100\times \left ( \frac{340}{340-40} \right )\) f = 340/3Hz = 113 Hz So the correct answer isoption 2.

A source is moving towards the observer with the speed of 40 m/s and emitting the sound of frequency 100 Hz. Find the observed frequency by standing observer if the velocity of propagation of sound is 340 m/s.1. 89 Hz2. 113 Hz3. 110 Hz4. 230 Hz

Answer» Correct Answer - Option 2 : 113 Hz

CONCEPT:

Doppler Effect:Anincrease or decreasein the frequency of sound,light, or other waves that are observed by the observer due to movement ofthe source and observer towards (or away from) each other is known as Doppler Effect.

Theapparent frequencyheard by the observer is given by the formula:

\(f=f_0\left ( \frac{v\pm v_o}{v \pm v_s} \right )\)

where f is apparent frequency, f0is the original frequency of the source, v is the speed of sound in air, vsis the speed of the source, vois the speed of the observer.

CALCULATION:

Given that v = 340 m/s; vs= 40m/s (-ve) moving towards; v0= 0; f = 100 Hz

\(f=f_0\left ( \frac{v\pm v_o}{v \pm v_s} \right )\)

\(f=100\times \left ( \frac{340}{340-40} \right )\)

f = 340/3Hz = 113 Hz

So the correct answer isoption 2.

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