<span>Many power plants in the United States use fossil fuels like natural gas and coal to generate energy, while others use nuclear power. </span>
Electricity flows from positive to negative
Answer:
D
Explanation:i think but dont get mad if im wrong
Answer:

So then the difference of temperature across the material would be 
Explanation:
For this case we can use the Fourier Law of heat conduction given by the following equation:
(1)
Where k = thermal conductivity = 0.2 W/ mK
A= 1m^2 represent the cross sectional area
Q= 3KW represent the rate of heat transfer
is the temperature of difference that we want to find
represent the thickness of the material
If we solve
in absolute value from the equation (1) we got:

First we convert 3KW to W and we got:

And we have everything to replace and we got:

So then the difference of temperature across the material would be 
As we know that spring force is given as

here we know that
F = 4 N
x = 2 cm = 0.02 m
now from the above equation we will have


so the elastic constant of the spring will be 200 N/m