Question #618a2

1 Answer
Jul 6, 2015

Their electrical potential energy is 22,500 J.

Explanation:

The electric potential energy associated with two charges, q_1 and q_2, separated by a distance r can be written like this

U = k_e * (q_1 * q_2)/r, where

k_e - Coulomb's constant, equal to 9.0 * 10^(9)"N m"^2"C"^(-2).

As you can see, this is simply a plug-and-play problem in which you use the given values to determine U.

SInce one spere is 75 mm from point P and the other is 25 mm from the same point P, in opposite directions, it follows that the distance between them is equal to

r = 75 + 25 = "100 mm"

This means that their electric potential energy is

U = k_e * (q * q)/r

U = 9.0 * 10^(9)"N" * "m"^(cancel(2))/cancel("C"^2) * ((500 * 10^(-6))^2cancel("C"^2))/(100 * 10^(-3)cancel("m")

U = 9.0 * cancel(10^9) * 250000/100 * cancel(10^(-9))underbrace("N" * "m")_(color(blue)("=Joule"))

U = color(green)("+22,500 J")