Queston about how to figure out charge of two beads, they you are given info about a spring.?

Question

Trying to do this homework question, but cant figure it out, can any one help please????

You have a lightweight spring whose unstretched length is 4.0 cm. You're curious to see if you can use this spring to measure charge. First, you attach one end of the spring to the ceiling and hang a 1.0 g mass from it. This stretches the spring to a length of 5.0 cm. You then attach two small plastic beads to the opposite ends of the spring, lay the spring on a frictionless table, and give each plastic bead the same charge. This stretches the spring to a length of 4.5 cm.

Answer 1

F=k(q1q2)/r^2
However there is a problem with the statement of the problem
1. Determine a DFDFDSF DSD ASDASDADS sdfddff

In general the force between two charges can be defined as
F=u(q1q2)/r^2
u - universal constant
q1, q2 - point charges
r – distance between them

And the force that stretches the string is
F=kx

Then electric force must be equal to electric force

u(q1q2)/r^2=kx

Then

q1q2= kx r^2 / u

Since both charges are hopefully the same then

q=sqrt(k x r^2 / u)
x
since x1=5cm when .oo1 kg stretched it we have
k=mg/x1= .001 9.81/.05= 0.1962 N/m

the u= 8.988×109 N m^2 /C^2

Then the q=sqrt(k x r^2 / u) becomes (r=unstretched + stretched part of the spring)
q=sqrt(0.1962 N/m .045 (.045m + .04m)^2 /8.988×109 N m^2 /C^2 ) =
q=sqrt(7.097E-15)
q=8.42 E-8 Coulombs or C