Answer:
v' = 14.76 m/s
Explanation:
given,
frequency of the one truck = 206 Hz
apparent frequency ,f' = 189 Hz
speed of sound, v = 343 m/s
speed of observer (v_o)and source (v_s) = v'
now, using Doppler's effect
[tex]f' = \dfrac{v-v_o}{v+v_s}\ f[/tex]
[tex]f' = \dfrac{v- v'}{v+v'}\ f[/tex]
[tex]189 = \dfrac{343- v'}{343+v'}\ 206[/tex]
[tex]0.9174= \dfrac{343- v'}{343+v'}[/tex]
314.69 + 0.9174 v' = 343 - v'
1.9174 v' = 28.30
v' = 14.76 m/s
hence, the speed of the truck is equal to 14.76 m/s