HW #12 9/22 Replacement for Problem 61

EX#1:  A thin, spherical, conducting shell of 
radius R is mounted on an insulated support 
and charged to a potential -V.  An electron
is fired from point P a distance r from the 
center of the shell with an initial speed v_0, 
directed radially inward.  What is the value 
of v_0 chosen so that the electron will just 
reach the shell?