\input epsf
\nopagenumbers
\magnification=\magstep1

\noindent {\bf Problem statement} Electrons repel each other with a
force which is inversely proportional to the square of the distance
between them; call the proportionality constant $k$ in the units to be
used. Suppose one electron is fixed at $x=0$ on the $x-$axis.

\medskip

\noindent a) Find the work done in moving a second electron along the
$x-$axis from the point $x=10$ to the point $x=1$.

\medskip

\noindent b) Find the work done in moving the second electron along
the $x-$axis from the point $x=M$ to the point $x=1$.

\medskip

\noindent c) What happens to your answer in b) (which should depend on
$M$) as $M \to +\infty$?

\vfil\eject\end