Three equal point charges, each with charge 2.00 î¼c , are placed at the vertices of an equilateral triangle whose sides are of length 0.350 m . what is the electric potential energy u of the system? (take as zero the potential energy of the three charges when they are infinitely far apart.) use epsilon_0 = 8.85ã—10−12 f/m for the permittivity of free space.

U = 3.08 10¹¹ J

Explanation:

Let's apply to our case

        U = k q₁q₂/ r₁₂ + k q₂q₃ / r₂₃ + k q₁q₃ / r₁₃

Let's look for distances, in an equilateral triangle all sides are equal

         r₁₂ = r₂₃ = r₁₃ = L

In the exercise they give the value of the charges and the side of the triangle

        q₁ = q₂ = q₃ = 2.00 C

        L = 0.350 m

In this case all the charges are equal and the distances are also the same, the formula is

         U = k 3 q² / L

Let's calculate

          U = 8.99 10⁹  3 4/0.350

          U = 3.08 10¹¹ J

close lines strong magnet less close weaker

the old price per ounce is c/4.

the new price per ounce is c/3.6.

the ratio of the old price to the new one is

(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form