charges in a rectangle?

Question

Three charges are situated at three corners of a rectangle as follows:
Upper left corner: 7.0 microC.
Lower Left Corner: 2.1 microC.
Lower right corner: 4.2 microC.

The height of the rectangle is 2.4 cm and the length of the rectangle is 6.5 cm. The columb constant is 8.98755e9 NM^2/C^2. How much electrical potential energy would be expected in movign the 7.0 microC charge to infinity (in J).

Answer 1

Ok, here I supposed, that the last charge is in the other corner of the rectangle. I mean the fourth charge is at the upper right corner :

So, we need to find the distances from the three charges to the last charge.

The distance from the first charge to the last charge is : 6.5 cm

The distance from the second charge to the last charge is :

sqr(6.5^2 + 2.4^2) = 6.92 cm

the distance from the third charge to the last one is : 2.4 cm

Now that we have the distances, let's find the potential difference that these three charges make to the last one :

K*7*10^-6 / (6.5/100) + k*2.1*10^-6 / (6.92 / 100) + k*4.2*10^-6 / (2.4/100)

this will be = 28*10^5 Volts >>> V

Now, the potential energy at the last charge is : q*V

The potential energy to infinity = 0 Volts

So the electrical potential energy will be qV - 0 = 28*10^5*7*10^-6
= 19.6 C.Volts

So that's the answer 19.6, hope that will help you.