Halliday, Resnick & Walker — Electric Potential: Problem 28

28 A positron (charge $+e$, mass equal to the electron mass) is moving at $1.5 \times 10^7 \text{ m/s}$ in the positive direction of an $x$ axis when, at $x = 0$, it encounters an electric field directed along the $x$ axis. The electric potential $V$ associated with the field is given in Fig. 24-34. The scale of the vertical axis is set by $V_s = 500.0 \text{ V}$. (a) Does the positron emerge from the field at $x = 0$ (which means its motion is reversed) or at $x = 0.50 \text{ m}$ (which means its motion is not reversed)? (b) What is its speed when it emerges?