Sound level at distance of 15 m is given as 20 dB
so intensity at this distance is given as



now if we move closer to some some distance the sound level is now 50 dB
now the intensity is given as



now we know that



so now the distance from friend must be 47 cm
1) The average velocity is 56 m/min
2) The average velocity is -83 m/min
Explanation:
1)
The average velocity of an object is given by

where
d is the displacement (change in position)
t is the time elapsed
In the graph in the problem, the displacement corresponds to the distance, therefore to the change in the y-variable (
), while the time elapsed is the change in the x-variable (
), so the average velocity can be written as

At point A, we have:

At point B, we have:

So, we have

So the average velocity is

2)
In this part instead, we have the following:
At point F, we have:

At point H, we have:

So, we have

So the average velocity is

Learn more about velocity:
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Answer:
The wavelength of observed light on earth is 568.5 nm
Explanation:
Given that,
Velocity of spaceship 
Wavelength of laser 
We need to calculate the wavelength of observed light on earth
Using formula of wavelength






Hence, The wavelength of observed light on earth is 568.5 nm
D.
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