# Coulomb’s Law

I’m having a little trouble with this question.
https://isaacphysics.org/questions/electric_shapes?board=edd98140-4c60-4348-bc65-f796a0303eb4&stage=a_level
Suppose the length of the triangle at equilibrium is l_1 and for rectangle is l_2, then by equating the electric force to spring force, we have q_1^2=constant * l_1^3
q_2^2=constant* l_2^3
And by sqrt(3)/4*l_1^2=l_2^2, I have the final answer of q_1/q_2 as 1.87, but it isn’t the right answer. Could somebody please help me? Thank you!
Original post by Scarlett L
I’m having a little trouble with this question.
https://isaacphysics.org/questions/electric_shapes?board=edd98140-4c60-4348-bc65-f796a0303eb4&stage=a_level
Suppose the length of the triangle at equilibrium is l_1 and for rectangle is l_2, then by equating the electric force to spring force, we have q_1^2=constant * l_1^3
q_2^2=constant* l_2^3
And by sqrt(3)/4*l_1^2=l_2^2, I have the final answer of q_1/q_2 as 1.87, but it isn’t the right answer. Could somebody please help me? Thank you!

The question is a lot more complicated than that - you need to resolve forces into horizontal and vertical components and equate those to the relevant charges. I'm assuming that you've found the length of a side of the square in terms of the length of a side of the triangle. Once you have this, using the equation for electric force and the spring equation to equate either the horizontal or vertical components of forces to each other.