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# The force related to an inverse-square potential

APPHMC-UGNVEY

A particular potential energy field can be described by the function $U(x) = \frac 1 {x^2}$ for all real values of $x$, where $U(x)$ and $x$ are in standard units.

What is the force magnitude exerted on a particle at the position $x = 3$?

A

$\frac {1} {3}$

B

$\frac {2} {27}$

C

$\frac {1} {9}$

D

$\frac {2} {9}$

E

$\frac {2} {3}$