Question

A fighter jet is traveling at
515 m/s directly away from
a communication antenna
that broadcasts at 406 MHz.
What change in frequency
does the fighter jet observe?
(in Hz)​

Answer 1

Given info : A fighter jet is traveling at 515 m/s directly away from a communication antenna that broadcasts 406 MHz.

To find : the change in frequency observed by the fighter jet is ...

solution : from Doppler's effect, f' = f(1 - u/c)

here c is speed of light, u is speed of fighter jet and f is the frequency broadcast by antenna.

so, f' = f(1 - u/c)

⇒f'/f = 1 - u/c

⇒(f - f')/f = u/c

⇒∆f = fu/c

so change in frequency , ∆f = fu/c

now f = 406 × 10⁶ Hz , u = 515 m/s and c = 3 × 10^8 m/s

so, ∆f = (406 × 10^6 × 515)/(3 × 10^8)

= 69696.67 × 10^-2

= 696.9667 Hz ≈ 697 Hz

Therefore the change in frequency observed by the fighter jet is 697 Hz.