A proton is held at a fixed position. An electron is placed 0.85m away and released.
Find the electron's speed when it's 9.0mm from the proton.
What is the difference in P between the two positions? That will be the gain of KE.
PE=kqq/r at each position, or
Pe=kqq(1/.85-1/.90)
set that equal to 1/2 mv^2 solve for v.