You used density, because water/ice has a density of 1, and ice will sink in anything with a lesser density
The speed of a proton after it accelerates from rest through a potential difference of 350 V is
.
Initial velocity of the proton 
Given potential difference 
let's assume that the speed of the proton is
,
Since the proton is accelerating through a potential difference, proton's potential energy will change with time. The potential energy of a particle of charge
when accelerated with a potential difference
is,

Due to Work-Energy Theorem and Conservation of Energy - <em>If there is no non-conservative force acting on a particle then loss in Potential energy P.E must be equal to gain in Kinetic Energy K.E</em> i.e

If the initial and final velocity of the proton is
and
respectively then,
change in Kinetic Energy 
change in Potential Energy 
from conservation of energy,

so, 

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heat conduction is cut off by vacuum.
metal cover block light thereby protecting radiation
The vacuum layer is the better thermal insulator
Explanation:
Depending on how they conduct heat, materials can be classified into two types:
- Thermal conductos: these are materials that are able to transfer heat efficiently. Examples of thermal conductors are metals in general: in fact, when you heat one side of a metal bar, the other end becomes hot very fast; this means that the heat has been transferred very quickly across the metal rod
- Thermal insulators: these are materials that do not transfer heat well. In general, gases or rarefied substances are better insulators, because the particles are more spread apart, and therefore the heat (which is transferred by conduction through collisions between molecules) is transferred less efficiently, due to the large distance between the particles.
In this sense, vacuum is the best possible insulator. This is because vacuum contains no particles at all, so there cannot be transfer of heat by conduction (because there cannot be collisions between molecules), and therefore, vacuum is the best thermal insulator.
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Answer:
order d> a = e> c> b = f
Explanation:
Pascal's law states that a change in pressure is transmitted by a liquid, all points are transmitted regardless of the form
P₁ = P₂
Using the definition of pressure
F₁ / A₁ = F₂ / A₂
F₂ = A₂ /A₁ F₁
Now we can examine the results
a) F1 = 4.0 N A1 = 0.9 m2 A2 = 1.8 m2
F₂ = 1.8 / 0.9 4
F₂a = 8 N
b) F1 = 2.0 N A1 = 0.9 m2 A2 = 0.45 m2
F₂b = 0.45 / 0.9 2
F₂b = 1 N
c) F1 2.0 N A1 = 1.8 m2 A2 = 3.6 m2
F₂c = 3.6 / 1.8 2
F₂c = 4 N
d) F1 = 4.0N A1 = 0.45 m2 A2 = 1.8 m2
F₂d = 1.8 / 0.45 4.0
F₂d = 16 m2
e) F1 = 4.0 N A1 = 0.45 m2 A2 = 0.9 m2
F₂e = 0.9 / 0.45 4
F₂e = 8 N
f) F1 = 2.0N A1 = 1.8 m2 A2 = 0.9 m2
F₂f = 0.9 / 1.8 2.0
F₂f = 1 N
Let's classify the structure from highest to lowest
F₂d> F₂a = F₂e> F₂c> F₂b = F₂f
I mean the combinations are
d> a = e> c> b = f