C. Age structure. Hope I helped :)
The rate of acceleration of the crate would be 1 m/s^2 because the equation for force is F=ma and when you plug in your numbers you get 10=10a so a=1
Length of the pipe = 0.39 m
Third harmonic frequency = 1400 Hz
For the third harmonic:
Wavelength = 
The center of the open pipe will host a node and the nearest anti - node from the center will be at the 0.25 × wavelength
Distance from center = 0.25 × wavelength
Distance = 
Plugging the value of the length of the pipe (L) = 0.39 m = 39 cm
Distance = 
Distance from the center to the nearest anti - node = 6.5 cm
Hence, the nearest distance to the anti - node from the center = 6.5 cm
So, option C is correct.
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<u>Answer:</u> Below 12m of depth, the submarine has to submerge so that it would not be swayed by surface waves
<u>Explanation:</u>
To avoid the surface waves, a submarine has to submerge below the wave base. It is the position below which the motion of the waves is negligible.
This wave base is equal to half of the wavelength. The equation becomes:
Wave base = 
We are given:
Wavelength = 24 m
Putting values in above equation, we get:
Wave base = 
Hence, below 12m of depth, the submarine has to submerge so that it would not be swayed by surface waves