Question

What frequency is received by the ambulance after reflecting from a wall near the person watching the oncoming ambulance (as in the previous problem). The ambulance is moving at 104 km/h and emitting a steady 821-Hz sound from its siren? The speed of sound on this day is 345 m/s.

Answer 1

f=896Hz

Step-by-step explanation:

Given data

Vs(speed of the ambulance)={(104 km/h)*(1000m*(1 h/3600)}=28.9m/s

f(frequency of the ambulance siren)=821 Hz

v(speed of sound)=345 m/s

Vo(speed of the observer)=0 m/s

To find

f(The ambulance is approaching the person)

Solution

From Doppler effect

`f^(i)=((v+v_(o) )/(v-v_(s) ))f`

As the ambulance approaches the we assign a positive sign for speed "vs" of the ambulance

So

`f^(i)=((v+0)/(v-(+v_(s)) ) )f\\f^(i)=((v)/(v-v_(s) ) )f`

Substitute the values from given data

`f^(i)=((345m/s)/(345m/s-28.9m/s) )821Hz\\f^(i)=896Hz`