Question

When operating at and in the vicinity of an uncontrolled aerodrome for which an ATF has not been published, the correct frequency to use is?

a) 122.7
b) 122.8
c) 123.2
d) 123.3

Answer 1

The frequency received by observers at an air show when a jet approaches and then departs is altered by the Doppler Effect. Using the given speeds and frequencies, the observed frequencies can be calculated for both scenarios. These calculations show how relative motion affects sound perception.

Step-by-step explanation:

When an air show features a jet flying directly towards an observer, the frequency of the sound received by the observer is affected by the Doppler Effect. Given the jet's speed of 1200 km/h (which converts to 333.33 m/s), a sound frequency of 3500 Hz, and the speed of sound of 342 m/s:

(a) To find the frequency received by observers as the plane flies towards them, the formula for the Doppler Effect when the source is moving towards the observer is used:

f' = f(v + vo) / (v - vs)

,
where

f'

is the observed frequency,

f

is the emitted frequency,

v

is the speed of sound,

vo

is the speed of the observer (0 since they're stationary), and

vs

is the speed of the source, the jet.

(b) Conversely, when the jet is flying away, the observed frequency is:

f' = f(v - vo) / (v + vs)

. In both cases, the observed frequencies will be different from the emitted frequency due to the

relative motion

between the source and observer.