Given an equilateral triangle with different charges namely charge on A is negative 4nC; B is positive 2nC and C is 1nC. The sides are all equal with 20cm. How can you calculate the resultant field on A; the mutual potential energy of the system?

Field on A? it comes from charges at B, C.

You have to add the E=kq/.2^2 equation from charges at B and C as VECTORS.

I don't know what "mutual" potential energy is. Potential energy is at a specified point.

To calculate the resultant electric field at point A, due to the charges at points B and C, we can follow these steps:

Step 1: Calculate the electric field at point A due to the charge at point B.
The electric field at a distance, r, from a point charge, q, can be calculated using Coulomb's Law:

Electric Field (E) = (k * q) / r^2

where k is the electrostatic constant (k ≈ 9 × 10^9 Nm²/C²).

In this case, the distance between point B and point A is the same as the length of the side of the equilateral triangle, which is 20 cm (or 0.2 meters).

Using the formula, we can calculate the electric field at point A due to the charge at point B:

Electric Field at A due to B = (9 × 10^9 Nm²/C²) * (2 × 10^(-9) C) / (0.2 m)^2

Step 2: Calculate the electric field at point A due to the charge at point C.
The method for calculating the electric field at point A due to the charge at point C is the same as in step 1. Since the distance between point C and point A is also 20 cm (or 0.2 meters), we can calculate it using:

Electric Field at A due to C = (9 × 10^9 Nm²/C²) * (1 × 10^(-9) C) / (0.2 m)^2

Step 3: Calculate the total electric field at point A.
Since electric fields are vectors, we need to calculate the vector sum of the electric field at point A due to charges B and C. As the triangle is equilateral, the electric fields due to B and C will have the same magnitude but opposite directions.

Therefore, we can use the formula:
Resultant Electric Field at A = Electric Field at A due to B - Electric Field at A due to C

Step 4: Calculate the mutual potential energy of the system.
The mutual potential energy of the system is given by the formula:

Mutual Potential Energy = (k * |q1 * q2|) / r

where q1 and q2 are the magnitudes of the charges, and r is the distance between them.

In this case, we have two pairs of charges: B and C, and A and B. The distances between these pairs are each 20 cm (or 0.2 meters). We can calculate the mutual potential energy for each pair separately, and then sum them up to get the total mutual potential energy of the system.

Mutual Potential Energy of B and C = (9 × 10^9 Nm²/C²) * (|2 × 10^(-9) C * 1 × 10^(-9) C|) / (0.2 m)

Mutual Potential Energy of A and B = (9 × 10^9 Nm²/C²) * (|-4 × 10^(-9) C * 2 × 10^(-9) C|) / (0.2 m)

Total Mutual Potential Energy = Mutual Potential Energy of B and C + Mutual Potential Energy of A and B

By following these steps, you can calculate the resultant electric field at point A and the mutual potential energy of the system.