# Conservation of Energy and electric potential

The figure shows a graph of electric potential versus position along the x-axis. An proton is originally at point A, moving along in the positive x-direction. How much kinetic energy does the proton need to have at point A in order to be able to reach point E ( with no forces acting on the proton other than those due to the indicated potential)? How much kinetic energy does the electron need? Points B, C, and D have to be passed on the way.

I don't have a copy of the graph, but

A = 100 V
B = 0 V
C = -60 V
D = -20 V
E = 55 V

Okay so I know that since positive charges move through decreases in potential, and the potential and potential energy are greatest at A, the proton will spontaneously travel from point A to point E. So, Ka = 0.

But I'm really not sure how to calculate the kinetic energy for the electron. If someone could help me out, I'd appreciate it!!!

Doc Al
Mentor
shorti2406 said:
Okay so I know that since positive charges move through decreases in potential, and the potential and potential energy are greatest at A, the proton will spontaneously travel from point A to point E. So, Ka = 0.
OK.

But I'm really not sure how to calculate the kinetic energy for the electron.
Realize that the electron needs enough initial energy to get past each intermediate point. How much energy is needed to get to B? (Measure the KE in electron volts; once you get your final answer you can convert units if you wish.) Is that enough to take it to C? Etc. (Hint: To the electron, a negative potential difference represents a barrier. What's the steepest barrier (lowest potential) that the electron must overcome?)