Question

Una sirena que emite un sonido de f=100Hz se mueve alejandose de un observador en reposo y dirigiendose hacia un acantilado con velocidad constante de v1=20 m/s.

Answer 1

Given that,

Frequency = 100 Hz

Velocity = 20 m/s

Suppose, Determinar la diferencia de frecuencia entre la onda que recibe el observador directamente de la sirena y la onda que le llega reflejada en el acantilado.

We need to calculate the frequency heard by the observer directly from source

Using formula of frequency

`f_(1)=f*((v)/(v-v_(s)))`

Where, v = speed of sound

`v_(s)` = speed of source

f = frequency of source

Put the value into the formula

`f_(1)=100*(340)/(340-20)`

`f_(1)=106.25\ Hz`

We need to calculate the frequency heard by the observer coming after reflection from cliff

Using formula of frequency

`f_(2)=f*((v)/(v+v_(s)))`

Put the value into the formula

`f_(2)=100*(340)/(340+20)`

`f_(2)=94.4\ Hz`

We need to calculate the difference of frequency

Using formula for difference of frequency

`\Delta f=f_(1)-f_(2)`

Put the value into the formula

`\Delta f=106.25-94.4`

`\Delta f=11.85\ Hz`

Hence, The difference of frequency is 11.85 Hz.