Respuesta :
There are several information's already given in the question. Based on those information's the answer can be easily deduced.
Speed of the truck = 70 kph
= 19.44 m/s
Speed of sound = 343 m/s
Then
Observed frequency = 400 Hz ∗ 343 m/s/19.44m/s + 343 m/s
= 378.54
= 379 Hz
Speed of the truck = 70 kph
= 19.44 m/s
Speed of sound = 343 m/s
Then
Observed frequency = 400 Hz ∗ 343 m/s/19.44m/s + 343 m/s
= 378.54
= 379 Hz