Can Physics hear my cry ?

Classical Mechanics Level 2

The driver of a car travelling with a speed of 30 ms − 1 30 \text{ ms}^{-1} towards a hill sounds a horn of frequency 600 Hz . 600\text{ Hz}. If the velocity of the sound in air is 330 ms − 1 , 330\text{ ms}^{-1}, then the frequency (in Hz \text{Hz} ) of the reflected sound as heard by the driver is __________ . \text{\_\_\_\_\_\_\_\_\_\_}.


The answer is 720.

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Parag Zode by Parag Zode , 24, India

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1 solution

Parag Zode
Mar 4, 2015

V = 330 m s − 1 V=330 ms^{-1} = Speed of sound in air.

V c = 30 m s − 1 V_{c}=30 ms^{-1} = Speed of car.

v o v_{o} =Frequency of horn.

Using the relation ,

v = V + V c V − V c . v o v=\dfrac{V + V_{c}}{V - V_{c}} . v_{o} ,we get

v = 330 + 30 330 − 30 . 600 v=\dfrac{330 + 30}{330 - 30} .600

v = 720 H z v=\boxed{720 Hz}

6 Helpful 0 Interesting 1 Brilliant 2 Confused

Are you sure the formula is correct?

Rishik Jain - 5 years, 2 months ago

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This is the only formula which we can use.

Parag Zode - 5 years, 2 months ago

Thanks. Simple and useful, that’s what we need

Batuhan Demir - 2 years, 4 months ago

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