Calculating the Effective Spring Constant of a Charged DNA Molecule

[Kdapik]

A molecule of DNA (deoxyribonucleic acid) is 2.09 µm long. The ends of the molecule become singly ionized: negative on one end, positive on the other. The helical molecule acts like a spring and compresses 1.09% upon becoming charged, and remains in this equilibrium position. Determine the effective spring constant of the molecule. I did calculate F and I got 5.27*10^-17 then I found x which is 2.27*10^-8
I found k from the equation k= f/x
I got 2.31*10^-9 N/m
But still, it's the wrong answer :(

 

[TSny]

Hello Kdapik. Welcome to PF!

I get a somewhat larger value for the force F. What did you use for the distance between the charges when you calculated F?

 

[Kdapik]

Hello Kdapik. Welcome to PF!

I get a somewhat larger value for the force F. What did you use for the distance between the charges when you calculated F?

2.06*10^-6 m

 

[TSny]

OK, that's pretty close to what I get (2.07 x 10^-6 m). I still don't see how you are getting 5.27 x 10^-17 N for the force. Can you show all the numbers that you used to get F?