Question

Two oppositely charged spheres, with a centre to centre separation of 4.0 cm, attract each other with a force of magnitude 1.2x10^-9N. The magnitude of the charge on one sphere is twice the magnitude the charge on the other. Determine the magnitude of the charge on each.

I tried to solve for the variable using the equation
1.2x10^-9=(k(x)(2x))/0.04^2 k is the constant so it equals 9.0x10^9 I tried solving it, but it did not work out.

Answer 1

I've been trying to do the problem on my own, but I just don't get it; please help me with it.

Answer 2

Your method looks OK to me. Let the charges be q and 2q.

1.2*10^-9 N = k *2 q^2/ r^2
k = 9.0*10^9 N m^2/C^2
r = 4.0*10^-2 m

q^2 = (1/2)(0.04)^2 * 1.2*10^-9/9.0*10^9
= 1.06*10^-22 C^2
q = 1.03*10^-11 C
The other particle has twice that charge.