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

Answer:

f=896Hz

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

$f^{i}=(\frac{v+v_{o} }{v-v_{s} })f$

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

So

$f^{i}=(\frac{v+0}{v-(+v_{s}) } )f\\f^{i}=(\frac{v}{v-v_{s} } )f$

Substitute the values from given data

$f^{i}=(\frac{345m/s}{345m/s-28.9m/s} )821Hz\\f^{i}=896Hz$