Answer:
The time elapses until the boat is first at the trough of a wave is 4.46 seconds.
Explanation:
Speed of the wave, v = 59 km/h = 16.38 m/s
Wavelength of the wave, 
If f is the frequency of the wave. The frequency of a wave is given by :

The time period of the wave is given by :

We need to find the time elapses until the boat is first at the trough of a wave. So, the time will be half of the time period of the wave.

Hence, this is the required solution.
Answer: Noise above 70 dB can cause hearing damage
Explanation:
Given that,
radius, r = 4.23 x 10∧7 m
Period, T = ?
Since, we know that,
In a geosynchronous satellite, period is equal to the period of earth that is 24 hrs.
Therefore, Time period is equal to 24 hours.