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GR0177 #59
Problem
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Electromagnetism$\Rightarrow$}LC Circuit

The form for a simple harmonic oscillator is $m\ddot{x} + kx =0$, which one can obtain from Hooke's Law. Comparing this to the LC circuit equation $L\ddot{Q}+Q/C=0$, one sees that $L \Leftrightarrow m$ and $1/C \Leftrightarrow k$ and $Q \Leftrightarrow x$. This is choice (B).

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theperiodictable
2014-10-23 11:05:59
One good thing to consider for this problem is the following: the only thing you can have a derivative of is x, since m and k are constants, so Q must be x.
bslugger360
2013-08-11 16:21:51
Another thought that helped me was looking at the energy of a spring and the energy of a capacitor:

$U_{capacitor} = \frac{Q^2}{2C}$

$U_{spring} = \frac{kx^2}{2}$

From this it's pretty clear that Q$\Rightarrow$x and C$\Rightarrow$1/k, making B the only possible answer.
mrTrig
2010-11-09 00:43:49
Something nice to remember $\omega = \frac{1}{\sqrt{LC}}$ for LC Circuits. And from hook's $\omega = \sqrt{\frac{k}{m}}$. Thus L and C must be inversely related and must be related to either $k$ or $m$. Only B satisfies.
carl_the_sagan
2008-11-07 19:48:26
A really cheesy way is to totally disregard the question and just look at the answers. Typically on a question like this they are going to have to repeat the correct value for each column a few times.

so "m" is repeated in L, "1/k" is repeated in C, and "x" is repeated in Q. The only answer which lines all these multiple-occurring rows is B.

Granted this has nothing to do with physics, but this isn't about physics, its about getting the right answer.
 amber2014-10-22 23:27:03 I went with this route too. I figured if there were two that were close I could reason it out, but I didn't have to do that.
 UNKNOWNUMBER2018-10-18 21:06:34 I don\'t think this works all the time--I would say you just got lucky.

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