# A molecule of DNA

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A molecule of DNA (deoxyribonucleic acid) is 2.10 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 1.29% upon becoming charged. Determine the effective spring constant of the molecule.

I keep getting within 10% and can't figure out where I'm going wrong.

asked Jan 12, 2014 in Others

The charge of an electron is 1.6*10-19C.  "singly ionized" means the charge both ends of the molecule is e (1.6*10-19C). the "r" is the length of a DNA molecule. According to Coulomb equation F=kQ1Q2/r^2, we got the force.Then, F=kx, where x is given (the molecule is compressed 1.29%).

If it is with 10%, just keep trying with 2 sigfigs.

p.s. I'm just a student but I got it right:) If you are done with Question 11 Plz help me! thanks!

answered Jan 12, 2014 by (1,010 points)
That's what I did but it's still wrong. Must be a webassign problem
Actually I just tried for 4 times and then I got it. (my calculator shows it should be 2.454e-9, then I tried 2.45, 2.4, and finally I tried 2.5e-9, it was right).
BTW, webassign sucks.