THere is a standard relationship that gives this result where the capacity of the capacitor is used:

.
We know though that Q/c=V and thus we can use the relationship:
E=Q*V/2 where we have just substituted in. If we also take into account that Q=VC, we can also get that E=V^2*C/2.
We are given the charge and the potential, so the best expression to use is the middle one.
Substituting, we get that E=1/2*8*10^(-10)*20=8*10^(-9).
The answer is B
Answer: The thermal efficiency of the engine is 41.09 %.
Explanation:
Efficiency is the ratio of the useful work performed to the total energy expended or heat taken in.
Formula for thermal efficiency of engine is

= efficiency
= heat rejected = 266.7 kJ
= heat extracted = 452.8 kJ
Putting in the values we get:



The thermal efficiency of the engine is 41.09 %.
Answer:
Explanation:
Incomplete question but for understanding.
We want to find the electrical force between two charges, then you can use the coulombs law which states that the force of attraction or repulsion between two charges is directly proportional to the product of the two charges and inversely proportional to the square of their distance apart,
So,
F = kq1•q2 / r²
Where k is a constant and it is given as
K = 8.99 × 10^9 Nm²/C²
q1 and q2 are the charges and in this question it is not given, so the question is incomplete. Let assume that,
q1 = - 1.609 × 10^-19 C electron
q2 = 1.609 × 10^-19 C proton
Since unlike charges attract, then it is force of attraction
Also, r is the distance apart and it is not given, let assume the distance between the two charges is 2 × 10^-5m
Then,
F = kq1•q2 / r²
F = 8.99 × 10^9 × 1.609 × 10^-19 × 1.609 × 10^-19 / (2 × 10^-5)²
F = 5.82 × 10^-19 N