how much external energy is required to bring three identical point charges (20uc) from infinity and place them at the corners of an equilateral triangle with side of 2 meter length:

U = 269.4 kJ

Explanation:

The energy required to place the three charges from infinity is given by:

In this case, you have that

q1 = q2 = q3 = q = 20uC

r12 = r13 = r23 = r = 2m

k: Coulomb constant = 8.98*10^9 NM^2/C^2

Then, you replace the values of q, r and k in the equation for the energy U:

hence, the required energy is 269.4 kJ

newton's first law of motion

it is the second option.