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 109 km/h and emitting a steady 821-Hz sound from its siren

Answer 1

900.48925 Hz

979.9785 Hz

Step-by-step explanation:

`v_a` = Relative velocity of ambulance =
`109\ km/h=(109)/(3.6)`

`v_w` = Velocity of wall = 0

v = Velocity of sound in air = 343 m/s

From doppler effect we have

`f=f'(v+v_w)/(v-v_a)\\\Rightarrow f=821(343+0)/(343-(109)/(3.6))\\\Rightarrow f=900.48925\ Hz`

The frequency of sound is 900.48925 Hz

When the wall acts like a source

`f=f'(v+v_a)/(v-v_w)\\\Rightarrow f=900.48925(343+(109)/(3.6))/(343-0)\\\Rightarrow f=979.9785\ Hz`

The frequency of sound is 979.9785 Hz