Answer:
31.4 mm²
Explanation:
The ability of a telescope or eye to gather light can be expressed by the formula,

where d signifies the diameter of the pupil.
In bright daylight, the usual size of the pupil is 3 mm.

Conversely, in darkness, the diameter typically enlarges to 7 mm.

This indicates an increase in light-gathering capacity.

Thus, the amount of light the eye can capture is 31.4 mm².
When the boat submerges completely in the pond, the water level of the pond rises.
Answer:
a) 
b) D does not influence the long-term results.
Explanation:
Given that

A = A0 cos(ωt)

This is a linear equation hence the integration factor, I

Now using the characteristics of linear equations


b) At t= 0

Thus, the initial condition
does not affect the long-term outcome.

Answer:
F=126339.5N
Explanation:
To compute the force required to escape, a free-body diagram for the hatch must be drawn. We will equate the downward and upward forces, thus applying the following equation:
Fw=W+Fi+F
where
Fw= force or weight exerted by the water column above the submarine.
To calculate Fw, we can use:
Fw=h. γ. A
h=height
γ=
specific weight of seawater = 10074N / m ^ 3
A=Area
Fw=28x10074x0.7=197467N
w represents the hatch weight = 200N
Fi denotes the internal pressure force in the submarine, which is 1 atm = 101325Pa. We can calculate this force using:
Fi=PA=101325x0.7=70927.5N
Finally, the force needed to open the hatch is determined by the original equation:
Fw=W+Fi+F
F=Fw-W+Fi
F=197467N-200N-70927.5N
F=126339.5N
Answer:
The water level increases more when the cube is above the raft before it sinks.
Explanation:
The principle involved is based on Archimedes' theory, which states that immersing an object in water will raise the initial water level. This means that the height of the water in the container increases. The increase in water volume corresponds to the volume of the submerged object.
We can consider two scenarios: when the steel cube rests on the raft and when it settles at the pool's bottom.
When the cube rests at the pool’s bottom, the volume will indeed rise, and we can ascertain this using the cube's volume.
Vc = 0.45*0.45*0.45 = 0.0911 [m^3]
When an object floats, it's because the densities of the object and water are in equilibrium.
![Ro_{H2O}=R_{c+r}\\where:\\Ro_{H2O}= water density = 1000 [kg/m^3]\\Ro_{c+r}= combined density cube + raft [kg/m^3]](https://tex.z-dn.net/?f=Ro_%7BH2O%7D%3DR_%7Bc%2Br%7D%5C%5Cwhere%3A%5C%5CRo_%7BH2O%7D%3D%20water%20density%20%3D%201000%20%5Bkg%2Fm%5E3%5D%5C%5CRo_%7Bc%2Br%7D%3D%20combined%20density%20cube%20%2B%20raft%20%5Bkg%2Fm%5E3%5D)
The formula for density is:
Ro = m/V
where:
m= mass [kg]
V = volume [m^3]
The buoyant force can be calculated with this equation:
![F_{B}=W=Ro_{H20}*g*Vs\\W = (200+730)*9.81\\W=9123.3[N]\\\\9123=1000*9.81*Vs\\Vs = 0.93 [m^3]](https://tex.z-dn.net/?f=F_%7BB%7D%3DW%3DRo_%7BH20%7D%2Ag%2AVs%5C%5CW%20%3D%20%28200%2B730%29%2A9.81%5C%5CW%3D9123.3%5BN%5D%5C%5C%5C%5C9123%3D1000%2A9.81%2AVs%5C%5CVs%20%3D%200.93%20%5Bm%5E3%5D)
Vs > Vc indicates that the combined volume of the raft and the cube exceeds that of the cube alone resting at the bottom of the pool. Hence, when the cube is positioned above the raft, the water level rises more before it becomes submerged.