Answer:

Explanation:
The period of a physical pendulum is:



The length of the leg is approximately the height of the person:

The period is:


Answer:
Doppler Theory
Explanation:
it's a theory regarding the change in wave frequency during the relative motion between a wave source and its observer.
Answer:
when the momentum of the vehicle moving at 30 km/h is higher than the one from the vehicle moving at 60 km/h
Explanation:
It's much harder to stop a freight truck moving at 30 km/h than a hot wheels car moving at 60 km/h.