Past exam of the physics 1 paper of the University of Oxford / 2013 resit / 9 / c / Solution

For $\theta =30^{\circ }$, the result in b gives $1/3=2E_0/(E+E_0)$, hence $E=5E_0$. Acceleration from rest supplies only the change in kinetic energy:The accelerating electric potential difference is a magnitude; its sign depends on which electrode is taken as the reference, since the electron has negative electric charge.