Final answer:
The frequency behavior heard by an observer below when a buzzer with frequency f0 is thrown straight upward and trips downward is lower than the actual frequency f0.
Step-by-step explanation:
The frequency behavior heard by an observer below when a buzzer with frequency f0 is thrown straight upward and trips downward can be determined using the concept of the Doppler effect. When a source moves towards an observer, the observed frequency is higher than the actual frequency of the source. Conversely, when the source moves away from the observer, the observed frequency is lower. In this case, as the buzzer travels downwards, it is moving away from the observer. Therefore, the frequency behavior heard by the observer below would be lower than the actual frequency f0.
The correct answer is option C) 1/2f0.