Answer:
21.7 m/s
Explanation:
Let the velocity of ambulance is v and f is the real frequency of siren of ambulance.
the velocity of sound is 343 m/s
use the formula of Doppler's effect
[tex]f' = \frac{343}{343-v}f[/tex] .... (1)
where, f' is the frequency of at the first time.
Now the source is moving away from the person, the frequency is given by
[tex]f'' = \frac{343}{343+v}f[/tex] .... (2)
According to the question,
f'' = f' - 11.0 % of f'
f'' = 0.881 f'
By equation (1) and (2)
[tex]\frac{343}{343+v}f= \frac{343}{343-v}\times 0.881f[/tex]
40.817 = 1.881 v
v = 21.7 m/s
Thus, the speed of ambulance is 21.7 m/s.
